Order of adverb "immediately" in a phrase

I’ve been struggling with this aspect of the English language and i don’t know if there are some rules to it that can help me. I’ve looked for answers on the internet but so far i haven’t found anything that can help me clear my mind on this issue.

I was writing this phrase :

“I called at your offices immediately to report the situation and I was assured that it would be repaired soon”

Is there a rule of when the “immediately goes”?

I could rephrase it into this:

“I immediately called at your offices to report the situation and I was assured that it would be repaired soon”

Or even:

“I called immediately at your offices to report the situation and I was assured that it would be repaired soon” (a grammar tool i have on my computer suggests in this particular phrase to change the at to a “to”)

Are any of those interchangeable?

Thanks in advance