Learn English – Is resolved vs has been resolved

"I will have been 7 years in the country this October"

...is fine, but I'd rejig it a bit, so:

"I will have been in the country seven years this October".

For the second, you could say:

"Last October was the start of my eighth year in the country".

You can use have been when something has just recently ended. For instance, you would say:

I'm exhausted because I've been in meetings all day.

was would also be acceptable, but I don't think it's as common in this case.

But if it was in the more distant past, you must use was:

I didn't get any writing done yesterday because I was stuck in meetings all day.

It would be wrong to use have been here.