Liên hệ bộ phận chăm sóc khách hàng; giữ hóa đơn.

It is an instructional / imperative sentence. Vietnamese often gives instructions by using the bare verb with no subject, especially in notices, labels, customer-service messages, and manuals.

So here:

• Liên hệ ... = Contact ...
• giữ hóa đơn = keep the receipt/invoice

Vietnamese does not need to say you. The subject is understood from context.

In Vietnamese, commands and instructions often omit the subject completely.

English usually says:

• Contact customer service and keep the receipt.

Vietnamese can simply say:

• Liên hệ bộ phận chăm sóc khách hàng; giữ hóa đơn.

This sounds natural in instructions. If you wanted to make it more explicit or softer, you could add words like:

• Hãy liên hệ... = Please / Do contact...
• Bạn hãy liên hệ... = You should / please contact...

But in signs, notices, and product instructions, leaving out you is very common.

Liên hệ means to contact, to get in touch with, or sometimes to reach out to.

In this sentence:

• Liên hệ bộ phận chăm sóc khách hàng = Contact customer service

A useful pattern is:

• liên hệ + person/department/company
  • liên hệ bác sĩ = contact the doctor
  • liên hệ công ty = contact the company
  • liên hệ bộ phận hỗ trợ = contact the support department

In everyday speech, people also say:

• liên lạc với... = get in touch with...
• gọi... = call...

But liên hệ is especially common in formal or written instructions.

Literally, it breaks down like this:

• bộ phận = department, section, division
• chăm sóc = care for, take care of
• khách hàng = customer(s)

So:

• bộ phận chăm sóc khách hàng = customer service department
• more literally: the department that takes care of customers

This is a very common formal expression in Vietnamese. You may also see:

• dịch vụ khách hàng = customer service
• trung tâm chăm sóc khách hàng = customer care center

Vietnamese noun phrases usually put the main noun first and then add words that describe or specify it.

Here:

• bộ phận = the main noun (department)
• chăm sóc khách hàng = what kind of department it is

So the order is:

• department + customer care

not:

• customer care + department

This is normal Vietnamese word order. Compare:

• công ty bảo hiểm = insurance company
• trung tâm y tế = medical center
• vé máy bay = airplane ticket

The broad category comes first, and the specifying phrase comes after it.

Giữ means to keep, to hold onto, or to retain.

So:

• giữ hóa đơn = keep the receipt/invoice

In this context, it means do not throw it away, because you may need it later.

Common examples:

• giữ vé = keep the ticket
• giữ biên lai = keep the receipt
• giữ bình tĩnh = keep calm

Vietnamese uses giữ very naturally for the idea of keeping something in your possession.

It can mean either invoice or receipt, depending on context.

Most broadly:

• hóa đơn = bill / invoice / receipt

In a customer-service or return/warranty context, English might translate it as receipt. In business or accounting contexts, it may be closer to invoice.

Related words:

• biên lai = receipt, proof of payment
• hóa đơn VAT = VAT invoice
• hóa đơn mua hàng = sales invoice / purchase receipt

So the exact English choice depends on the situation, even though the Vietnamese word stays the same.

The semicolon separates two short instructions:

1. Liên hệ bộ phận chăm sóc khách hàng
2. giữ hóa đơn

It works like a stronger pause than a comma. In English, this might be written as:

• Contact customer service; keep the receipt.
• or Contact customer service and keep the receipt.

In Vietnamese notices and formal writing, punctuation like this is often used to present instructions clearly and compactly.

Yes. You could say:

• Liên hệ bộ phận chăm sóc khách hàng và giữ hóa đơn.

That would mean the same thing: Contact customer service and keep the receipt.

However, using a semicolon makes it feel more like two separate checklist-style instructions. That style is common in notices, packaging, and policy language.

So:

• ... và ... = more like one connected sentence
• ... ; ... = more like two parallel instructions

Both are understandable.

Adding hãy would make the instruction more explicitly imperative, similar to please or do in English.

For example:

• Hãy liên hệ bộ phận chăm sóc khách hàng; hãy giữ hóa đơn.

This is grammatical, but in practical written instructions Vietnamese often leaves hãy out because the command meaning is already obvious.

So:

• Liên hệ... = concise, neutral instruction
• Hãy liên hệ... = more explicitly telling someone to do it

In warnings, labels, and customer instructions, the shorter version is very common.

It sounds neutral to formal, especially because of the phrase bộ phận chăm sóc khách hàng.

Reasons it sounds formal:

• liên hệ is more formal than just gọi (call)
• bộ phận chăm sóc khách hàng is an organizational/business expression
• the sentence is short and instruction-like

A more casual version might be something like:

• Gọi chăm sóc khách hàng và giữ lại hóa đơn.

But the original sentence is exactly the kind of wording you would expect in official customer-service instructions.

Yes. Giữ lại hóa đơn is also very natural.

• giữ hóa đơn = keep the receipt
• giữ lại hóa đơn = keep/hold on to the receipt

The particle lại often adds the feeling of keeping something rather than discarding it.

So in many contexts:

• giữ hóa đơn
• giữ lại hóa đơn

both work, but giữ lại may sound slightly more explicit, like keep it for later.

In natural speech, it would sound something like two short instruction units:

• Liên hệ bộ phận chăm sóc khách hàng // giữ hóa đơn.

A learner should notice a few things:

• liên hệ has two separate syllables: liên
  • hệ
• bộ phận also has clear separate syllables
• khách hàng has a natural stress-like emphasis from sentence rhythm, even though Vietnamese does not use stress like English
• giữ hóa đơn is often spoken smoothly as a short chunk

Vietnamese is syllable-timed, so it helps to practice it in chunks:

• liên hệ
• bộ phận
• chăm sóc khách hàng
• giữ hóa đơn