Замість того щоб телефонувати продавцеві, написав службі підтримки.

Because замість on its own normally goes with a noun or pronoun:

• замість дзвінка = instead of a call
• замість мене = instead of me

When Ukrainian wants to say instead of doing something, it very often uses the set expression замість того щоб + verb.

So:

• замість того щоб телефонувати = instead of calling

The version замість телефонувати is not standard here.

In this pattern, замість того щоб + infinitive is very common when the same person is understood in both parts of the sentence.

So the idea is:

• Instead of calling the seller, (he/I) wrote to support.

The subject of телефонувати is the same as the subject of написав.

If you wanted to name a different subject, Ukrainian could use a finite verb instead, for example:

• Замість того щоб він телефонував продавцеві... = Instead of him calling the seller...

But in your sentence, the infinitive is the natural choice.

Ukrainian very often drops subject pronouns when the subject is clear from context.

So написав can stand by itself.

One important detail: in the past tense, написав shows gender and number, but not person clearly. It tells you the subject is masculine singular, but context must tell you whether it means:

• I wrote (if the speaker is male), or
• he wrote

Compare:

• написав = masculine
• написала = feminine
• написали = plural

So the missing subject is normal Ukrainian style.

Продавцеві is in the dative case.

The verb телефонувати usually takes the dative:

• телефонувати кому? = to call whom?

So:

• телефонувати продавцеві = to call the seller

A common alternative dative form is продавцю. Both are possible:

• продавцеві
• продавцю

Both mean the same thing; the choice is often stylistic.

For the same reason: написати can mean to write to someone, and that recipient is often in the dative case.

• написати кому? = to write to whom?

So:

• написав службі = wrote to the service

Then підтримки is part of the noun phrase служба підтримки = support service.

Only the main noun changes for the dative:

• служба підтримки → nominative
• службі підтримки → dative

So підтримки stays as it is because it depends on служба and is already in the form needed inside that phrase.

Not necessarily. In Ukrainian, писати / написати комусь often simply means to write to someone.

So:

• написав службі підтримки = wrote to customer support

The exact thing written is omitted because it is obvious from context, just like in English:

• I wrote to support.

You do not have to add лист, повідомлення, etc. unless you specifically want to mention it.

This is about aspect.

• писати = imperfective
• написати = perfective

So:

• писав = was writing / wrote (with focus on process, repetition, or no clear completion)
• написав = wrote, completed the action

In your sentence, написав is natural because it presents a completed result: instead of calling, the person sent/wrote a message to support.

If you used писав, it would sound more like focusing on the process or ongoing action.

This is also aspect.

• телефонувати = imperfective
• зателефонувати = perfective

In a phrase like замість того щоб телефонувати, the imperfective often sounds more general:

• instead of calling / instead of making calls / instead of trying to call

It presents the action as an option or type of action.

If you said:

• замість того щоб зателефонувати продавцеві

that would be more like:

• instead of making that one call to the seller

So the imperfective here is very natural, though the perfective can also be possible if you want that more one-time, completed sense.

The comma after продавцеві separates the opening instead of... phrase from the main part of the sentence:

• Замість того щоб телефонувати продавцеві, написав службі підтримки.

As for того щоб, Ukrainian can treat замість того щоб as a single complex connector, so no comma is required inside it in this version.

You may also sometimes see a split version:

• замість того, щоб ...

That also occurs in Ukrainian. In your sentence, the conjunction is simply being treated as one unit.

Yes, but it is also quite natural.

Ukrainian word order is flexible, and the sentence starts with:

• Замість того щоб телефонувати продавцеві...

because that is the contrastive idea: instead of doing X...

Then the main action comes after it:

• ...написав службі підтримки

This order highlights the rejected option first, then the action that was actually taken.

A different order is possible, but the given one is very normal and clear.