From what I've heard about DSL Pipex they are a competent communications company who are dabbling in new technology.
It sounds as though your provider is having teething problems with their new product, and are anxious to retain your custom while they sort out the glitches. It would be interesting to know how many other customers share your complaint.
If you haven't already done so it would be worthwhile obtaining the name of a person to whom you could write and spell out clearly your grievance. Telephone calls or on-line conversations can become emotionally charged, and that just gets in the way of what you are trying to achieve. Set out in writing a factual account of your position, make it clear what you want from them, but don't resort to rudeness or threats. Give the person a set time to reply to the points raised in your letter, and you might be surprised by the helpful feedback you receive. If the company is still uncooperative I suggest you contact your local Trading Standards office who can advise you further.
Good luck.
Davefingers.