I have two phone lines in my house (two BT twisted pairs). One is a business line, with AAISP FTTC. The other has Bulldog/Pipex ADSL2.
Since the Pipex line is only for backup now, I decided to downgrade it to a cheaper package, so I called BT and asked them to take over the line with a basic ADSL package.
Instead, they took over my business line, causing all my incoming calls to come in on that socket. When I called customer services, thay told me I was mistaken, and I only have one line. After a long time on the phone, with warnings about how I must pay if it's my fault, they agreed to send an engineer out. When he arrived, he didn't believe me either, until he took both sockets off the wall, and put his test equipment on it. He said it was an exchange fault, and I had to call customer services again. I wouldnt let him go until I called them, so he could explain it. But they didn't believe him either!! He ended up leaving while I was stuck on the phone to CS. 5 days later engineer two arrived, and said the same thing. I called CS again, and its just back to square one.
There doesn't seem to be any way out of this. AAISP tell me my business line doesn't exist any more!