Contactei a seguradora hoje.

In Portuguese, the subject pronoun is often left out because the verb ending already shows who is doing the action.

• contactei = I contacted
• The ending -ei tells you it is eu in the past

So Contactei a seguradora hoje is perfectly natural, and adding eu would usually only be for emphasis:

• Eu contactei a seguradora hoje = I contacted the insurance company today (with extra emphasis on I)

Contactei is in the pretérito perfeito simples, which is the normal past tense used for a completed action.

Here it means that the action happened and is finished:

• contactei = I contacted

This tense is very commonly used in European Portuguese for single completed actions in the past.

The infinitive is contactar.

This is a regular -ar verb, so in the first person singular of the pretérito perfeito simples, the ending becomes -ei:

• contactar → contactei

A few forms of the verb in this tense are:

• eu contactei
• tu contactaste
• ele/ela contactou
• nós contactámos
• vós contactastes
• eles/elas contactaram

So contactei simply means I contacted.

Here, a is the definite article, meaning the.

• a seguradora = the insurance company / the insurer

Because seguradora is a feminine singular noun, the article is a.

Compare:

• o banco = the bank
• a seguradora = the insurance company

So the a is not a preposition here. It is just the feminine singular word for the.

In Portuguese, nouns have grammatical gender. Seguradora is feminine, so it takes feminine articles and adjectives.

That is why you get:

• a seguradora
• not o seguradora

The word often refers to an insurance company or insurer. The feminine gender is a property of the noun itself, not necessarily of a female person.

Yes. Hoje is quite flexible in Portuguese.

All of these are possible:

• Contactei a seguradora hoje.
• Hoje contactei a seguradora.
• Contactei hoje a seguradora.

The most neutral choices are usually:

• Hoje contactei a seguradora
• Contactei a seguradora hoje

The version you were given sounds natural and clear.

Yes, contactar is completely natural in European Portuguese.

So Contactei a seguradora hoje is a normal sentence.

You may also hear:

• Entrei em contacto com a seguradora hoje = I got in touch with the insurance company today

Both are correct. Contactar is shorter and very common in everyday use.

These forms express different ideas.

• contactei = completed action, I contacted
• contactava = habitual, ongoing, or background action, something like I was contacting or I used to contact

In this sentence, the speaker means one finished action that happened today, so contactei is the right choice.

In European Portuguese, contactei is pronounced approximately like:

• con-tac-TEI

A few helpful points:

• the stress is on the last syllable: -tei
• the ending -ei sounds a bit like ay
• in European Portuguese, unstressed vowels are often reduced, so the first part may sound less open than an English speaker expects

Also, in Portugal, the spelling contactar and contactei is standard, and the c is kept because it is pronounced.

Usually, no, not for this meaning.

In European Portuguese, tenho contactado often suggests a repeated action over a period of time, something like:

• I have been contacting
• I have contacted repeatedly

But contactei hoje means a single completed action today:

• I contacted the insurance company today

So for this sentence, contactei is the natural choice.

Yes, but the meaning changes.

• a seguradora = the insurance company
  You mean a specific one, known from the context.
• uma seguradora = an insurance company
  You mean one insurance company, not previously identified.

So the original sentence refers to a specific insurer.

Most commonly here, seguradora means the insurance company or the insurer as an institution.

Depending on context, Portuguese can sometimes use related words for people or entities in different ways, but in everyday sentences like this one, learners should understand a seguradora as the insurance company.