Hi and welcome to the forum. Sorry to hear of your problems, and the fact Tesco aren't doing anything to help you.
As you say, your stats look pretty normal and certainly wouldn't be the cause of loss of sync for a few days.
If you've spent a year talking to Tesco's helpdesk, then you are a lot more patient than me! Having tried two different modems, I would be inclined to agree with you that it's a fault on your line.
Have you tried the quiet line test - dial 17070 and select the appropriate option (I think it's 2) and see if there's any background noise on your line - both in times when there is sync and when there isn't.
If that comes out ok, you have a few courses of action:
1. Send a written letter to Tesco explaining what's happened, and see what comes of it.
2. Complain and put your case to OFCOM and see what (if anything) they do about it.
3. Not sure if you can raise a fault on the line with BT, since if your telephone service is ok, and BT aren't your ISP, it's all a bit disconnected on that front within the BT group, and you may end up going round in circles.
If these fail, you have some more drastic options:
1. Appeal to the nature of BT's CEO by emailing him directly without complaining, given BT haven't really done anything wrong at this stage... (yes he or his office will respond). I won't tell you his email address but his name is Ben Verwaayen and his email is in the form of firstname.lastname @ bt.com
- I'd only do this as a last resort though, to be honest.
2. Move to an ISP who does actually care and who will raise the problem to BT for you!
Apart from that, I'm not really sure - it sounds like you're having a bit of a nightmare with this, and there's no way this could be called an acceptable broadband service. Failing Tesco, OFCOM
should be the ones who sort this out.
Good luck and keep us up to date