Maybe write 2 letters. 1 says what you really feel. Do not post it.
the second is the humble one, but with as amany hard facts as you can assemble.
I agree wholeheartedly with that advice.
It's easy to get so embroiled in your personal situation that it's not difficult to write a long rambling letter that doesn't really say anything.
If you have a known weakness with writing letters, perhaps also, if you can, show the letter to someone who knows absolutely no background to your situation (friend/relative whoever). See if they can understand just from one reading (giving them a time limit of, say 5 or 10 minutes) whether they can get a good understanding of what the problem is, and what has been tried before.
Oh, and don't forget to send it recorded delivery. BT get somewhere in the region of 800,000 letters per year, so recorded will at least (hopefully) get you somewhere higher up the pile in the mailroom !
The less work your case handler has to do to figure out what the problem is, and to get an idea of which departments he/she needs to speak to first, the better.
Once you have a case handler, be as nice as you possibly can to her/him. they are your way in.
Agree here too.
Particularly as a private individual, where your value to BT in a pure business sense (i.e. revenue) is largely irrelevant. Same goes for the fact that you're out in the sticks, where BT has no competition, you know that, and BT definitely know that !
So yes, grit your teeth.
And offer the BT engineer tea/coffee and cakes when he arrives, it works wonders.
I allowed my last BT pet engineer to watch a football match (and gave him a cold drink) whilst he was waiting for various callbacks from callcentres and exchanges that he had to call for that particular job.