hikkosigyousya ni asa hatizi ni kite moraukoto ni simasita.

Because ～てもらう marks the person or group you receive the action from with に.

So in:

• 引っ越し業者に来てもらう

the movers are the ones who will do the action of coming, and the speaker is the one who benefits from or arranges that action.

A very literal breakdown is:

• 引っ越し業者に = from the moving company / by the movers
• 来てもらう = have them come / get them to come

This is different from を, which would mark a direct object.

They do two different jobs.

• 引っ越し業者に
  marks who will perform the action in the ～てもらう pattern

• 朝八時に
  marks the time when the action happens

So even though they are both に, they are not the same kind of に.

来てもらう is the て-form + もらう pattern.

It means something like:

• to have someone come
• to get someone to come
• to have someone come for you

The key nuance is that the speaker sees the action as something done for their benefit or as something they arranged/requested.

Compare:

• 引っ越し業者が来る = the movers will come
• 引っ越し業者に来てもらう = I’ll have the movers come / I’ll get the movers to come

The second one sounds more like an arrangement or service that the speaker is making use of.

Because 来る only says that they come.
来てもらう adds the idea that the speaker is having them come as part of an arrangement.

Compare:

• 引っ越し業者が朝八時に来ることにしました
  = I decided that the movers will come at 8 a.m.

• 引っ越し業者に朝八時に来てもらうことにしました
  = I decided to have the movers come at 8 a.m.

The second version sounds more natural if you are talking about booking or arranging a service.

ことにしました means decided to do.

It is built from:

• verb dictionary form / verb phrase
• ことにする = to decide to do ...
• ことにしました = decided to do ...

So:

• 来てもらうことにしました

means:

• I decided to have them come
• or in context, I arranged for them to come

In real-life situations like this, ことにしました can sound close to I decided/settled on that plan.

Because the sentence is talking about the decision/arrangement, not the completed event itself.

• 来てもらいました = they came for me / I had them come
  This sounds like the coming already happened.

• 来てもらうことにしました = I decided to have them come
  This focuses on the plan or decision.

So if the movers are scheduled to come later, ことにしました is the natural choice.

Because Japanese often leaves out subjects and topics when they are understood from context.

Even without 私は, it is natural to understand that the speaker means something like:

• (私は) 引っ越し業者に朝八時に来てもらうことにしました。

Japanese frequently omits:

• I
• we
• he/she
• sometimes even objects

if they are obvious from the situation.

Japanese nouns usually do not mark singular vs. plural clearly.

So 引っ越し業者 could mean:

• a moving company
• the movers
• a moving service

In English, the best translation depends on context.
In this sentence, it could refer to either:

• the company as a service provider
• the workers who will come

Both are natural.

Both are possible, but 朝八時 is very common and natural.

• 朝八時に = at 8 in the morning
• 朝の八時に = at 8 in the morning

The version without の is concise and frequently used in schedules, plans, and everyday speech.

So:

• 朝八時に来てもらう

sounds perfectly normal.

こと turns the verb phrase into something noun-like, so it can be the object of 決める/する-type expressions.

Think of it like this:

• 来てもらう = have them come
• 来てもらうこと = the act/plan of having them come
• 来てもらうことにしました = decided on the act/plan of having them come

You do not need to translate こと every time, but grammatically it helps package the action into a decision.

Yes. The sentence ends in しました, which is polite past.

Notice that the earlier verbs stay in plain form:

• 来て
• もらう
• する → しました

That is normal in Japanese. Usually only the final verb shows the sentence’s politeness level.

So this is a standard polite sentence.

Grammatically you could build a sentence with 来させる, but it gives a very different nuance.

• 来てもらう = have them come / arrange for them to come / receive the favor/service
• 来させる = make/let them come

With a service provider like movers, 来てもらう is much more natural because you are arranging a service, not forcing them.

So 来てもらう is the better choice here.

A useful breakdown is:

• 引っ越し業者に = from/by the moving company
• 朝八時に = at 8 a.m.
• 来て = come
• もらう = receive that action / have them do it
• ことにしました = decided to do that

So the structure is basically:

• [person/service provider] に [time] に [verb-て] もらう ことにしました

This pattern is very useful for saying things like:

• 友達に手伝ってもらうことにしました。
  I decided to have a friend help me.

• 先生に見てもらうことにしました。
  I decided to have the teacher look at it.

• 業者に修理してもらうことにしました。
  I decided to have a company repair it.