I've been with Virgin since about 2002, and almost no problems until the current place. After I had five multi-day outages in a few months, I switched to one of the BT resellers (not plugging them 'till I know they're actually good).
Sometimes, you get wired through a bad cabinet (in my case, mucked up by years of landlords turning houses into 4-7 bed flats for students until the cabinet is 60% splitters by volume) and it'll just keep failing. Not much you can do, since they're not willing to put the effort in to actually fix it properly - they just unplug someone else and hope it's not in active use. Most of the customers on the box will move out next summer anyway.