Over 10 years of internet problems and helping neighbors/friends call BT, every time the call goes "We see no fault reported at the exchange, it must be your equipment."
Every time, the fault has been broken cables, cabinets and sockets at the exchange (I recently had to be plugged into a new exchange socket). With one exception (I was not involved ;) ) being a work college who had plugged in the routers wrong, but got let off the £120 charge as the engineer found another fault near by in the process.
Other companies are not even any better, as many over sell on capacity or blatantly lie about services and features.
I've gone with a smaller company who are as honest as they come. Sadly they do have to use BT backhual and last mile for most services.