Saya menghubunginya tadi malam.

Menghubungi is the active verb form, built from the root hubung with the prefix meng- and the suffix -i.

• hubung = connection / contact
• menghubungi = to contact someone

In a normal statement like Saya menghubunginya tadi malam, Indonesian usually uses the active meN- verb form.

Hubungi by itself is usually an imperative, meaning contact ...! or please contact ...
So:

• Saya menghubunginya = I contacted him/her
• Hubungi dia! = Contact him/her!

Here -nya means him, her, or sometimes them, depending on context.

So menghubunginya = contacted him/her.

This suffix is very common in Indonesian and can attach directly to verbs:

• melihatnya = see him/her
• mengenalnya = know him/her
• memanggilnya = call him/her

It does not show gender, so -nya can mean him or her.

Yes, absolutely.

Both are natural:

• Saya menghubunginya tadi malam
• Saya menghubungi dia tadi malam

The version with -nya is often a bit smoother and more compact. The version with dia is also very common and may feel slightly more explicit.

In Indonesian, tadi often refers to a time earlier than now, and combined with parts of the day it can indicate a recent past time.

• tadi pagi = earlier this morning
• tadi siang = earlier today / this afternoon
• tadi malam = last night / earlier last night

So tadi malam is the natural way to say last night in many contexts.

Indonesian often does not need a preposition where English does.

English says:

• I contacted him last night
• or at night in other contexts

Indonesian simply says:

• Saya menghubunginya tadi malam

Time expressions like kemarin, besok, tadi malam, and jam lima often appear directly without a preposition.

This is the normal Indonesian order:

Subject + Verb + Object + Time

So:

• Saya = subject
• menghubunginya = verb + object
• tadi malam = time expression

Indonesian time expressions are often placed at the end, though they can also be moved earlier for emphasis:

• Saya menghubunginya tadi malam
• Tadi malam saya menghubunginya

Both are correct.

The -i is a suffix that helps form the verb menghubungi from hubung. For learners, the most useful thing is to treat menghubungi as a complete dictionary verb meaning to contact.

In many Indonesian verbs, -i is associated with actions directed toward an object or involving repeated/location-related action, but with menghubungi, it is best learned as a fixed form:

• hubung → menghubungi = to contact

You do not normally say menghubung for this meaning.

No. You could also say aku in casual situations:

• Saya menghubunginya tadi malam = polite/neutral
• Aku menghubunginya tadi malam = more informal

Saya is the safer choice in most situations, especially with people you do not know well, in writing, or in formal speech.

Not exactly.

• menghubungi = to contact
• menelpon/menelepon = to telephone / to call

So menghubungi is broader. You can contact someone by phone, text, email, or another method.
If the meaning is specifically called on the phone, menelponnya may be more precise.

Yes, -nya can also mean it, depending on context. Indonesian -nya is very flexible.

For example:

• Saya membacanya = I read it / I read him/her
  depending on what -nya refers to

In Saya menghubunginya tadi malam, the most likely meaning is him/her, because contacting usually involves a person.

A rough pronunciation guide is:

meng-hu-bu-ngi-nya

A few helpful points:

• ng sounds like the ng in sing
• u is like oo in food
• ny sounds like Spanish ñ or the ny in canyon

So -nya sounds roughly like nya, not nee-ya.

Yes, that is also possible.

• Semalam saya menghubunginya = Last night I contacted him/her
• Saya menghubunginya tadi malam = I contacted him/her last night

Both are natural. Semalam is a single-word alternative to tadi malam in many contexts, though usage can vary a bit by region and style.

It is basically neutral to polite.

Why?

• Saya is polite/standard
• menghubungi is standard and natural
• tadi malam is everyday Indonesian

So this sentence works well in normal conversation, writing, and many semi-formal situations.
A more casual version might be:

• Aku menghubunginya tadi malam

A very formal sentence might depend on context, but this one is already perfectly normal and appropriate in standard Indonesian.