mixture's dislike of BT is well known and no doubt heartfelt and from experience given that he is in the business.
I was with a very good company called Nildram since 2002 and they were reliable and the service was consistent with a brilliant tech. helpline for the rare occasion when it was needed. Then Tiscali took over which became Talk/Talk and eventually I was transferred to Opal!
I suffered the same frustration and poor service from them as the OP when my speed fell through the floor. After a month of frustration I transferred to BT (Infinity) and so far it has been brilliant with outstanding customer service. I can only speak as I find but I can say anything with Talk/Talk associated with it makes me put on my running shoes and head in the opposite direction!