Okazis interrompo; tial mi telefonis al la provizanto.

In Esperanto, okazi means to happen / to occur, and it can be used in a fairly impersonal way.

So Okazis interrompo is literally something like:

An interruption happened
or
There was an interruption

Even though English often uses there was, Esperanto can simply use the verb first: Okazis interrompo.

Here:

• okazis = happened / occurred
• interrompo = interruption

So the noun interrompo is the thing that happened.

Interrompo is a noun meaning interruption, outage, or break in service, depending on context.

It comes from the verb interrompi = to interrupt.

The ending -o marks a noun:

• interrompi = to interrupt
• interrompo = interruption

In this sentence, it most naturally suggests some kind of service interruption, such as internet, electricity, or phone service.

Tial means therefore, for that reason, or that's why.

It points back to a cause:

• Okazis interrompo; tial mi telefonis...
• There was an interruption; therefore / for that reason I called...

A learner may compare it with do, which also often translates as so or therefore. The difference is that tial explicitly means for that reason, while do is a more general connector for consequence or continuation.

In careful, explanatory language, tial is often very clear and natural here.

The semicolon links two closely related independent clauses:

• Okazis interrompo
• tial mi telefonis al la provizanto

Each part could stand on its own, but they are strongly connected: the second is the result of the first.

A comma is sometimes seen in practice, but the semicolon helps show a stronger separation and makes the logic very clear.

In Esperanto, telefoni means to telephone / to call by phone.

So:

• mi telefonis = I telephoned / I called

This is a very normal way to express making a phone call. English uses call very broadly, but Esperanto often uses the more specific telefoni when the call is specifically by telephone.

Because telefoni normally takes al before the person or organization being called.

So:

• telefoni al iu = to phone someone

That means:

• mi telefonis al la provizanto = I phoned the provider

For an English speaker, this can feel unusual because English says call someone directly without a preposition. But in Esperanto, al is the standard pattern here.

Provizanto literally means supplier or provider.

It comes from:

• provizi = to supply / provide
• -anto = a person or entity that does the action

So:

• provizanto = one who provides

In this sentence, it likely means a service provider, such as an internet provider, electricity provider, or similar company.

Depending on context, Esperanto speakers might also choose a more specific term, but provizanto is understandable and natural for provider in many situations.

La is the definite article, meaning the.

It is used because the speaker has a specific provider in mind:

• la provizanto = the provider

This is natural if the listener can identify which provider is meant from context, such as the internet provider, the utility provider, etc.

Without la, provizanto would sound more like a provider or some provider, which is less likely here.

The ending -is marks the past tense in Esperanto.

So:

• okazis = happened / occurred
• telefonis = telephoned / called

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = imperative / jussive
• -i = infinitive

This is one of the easiest parts of Esperanto for English speakers, because the tense marking is always consistent.

Yes, Interrompo okazis is grammatically correct.

Both are possible:

• Okazis interrompo
• Interrompo okazis

The version with the verb first, Okazis interrompo, often sounds a bit more natural when introducing an event, similar to English There was an interruption.

So the chosen word order helps present the interruption as newly introduced information.

Not exactly.

These words can overlap, but they are not identical:

• interrompo = interruption, break, stoppage
• paneo = breakdown, failure, outage
• malfunkcio = malfunction

So interrompo focuses on the service being interrupted.
If the emphasis were on a technical failure, another word might be better.

For example:

• Okazis interrompo de la servo = There was a service interruption
• Okazis paneo = There was a breakdown/outage
• Okazis malfunkcio = There was a malfunction

In your sentence, interrompo works well if the idea is that service stopped and that is why the speaker called the provider.

Yes, Esperanto word order is fairly flexible, so you could move tial for emphasis.

For example:

• Okazis interrompo; tial mi telefonis al la provizanto.
• Okazis interrompo; mi tial telefonis al la provizanto.

Both are possible. The original version is especially clear because tial comes first in the second clause and immediately signals the logical result: therefore.

So the original wording is a very good, natural choice for learners to copy.