My advice would be to contact BT - telephone 0800 800 1540 from your mobile.
BT are not eh cheapest provider, but as with anything, you get what you pay for. I have had very little troubnle with my service,, any issues have always been recitifed quickly.
Other providers will offer cheaper rates, but from general conversation, it appears that their ability to provide continaul service, and to rectify any issues, are seriously below the service provided by BT.
Good luck.