The legal phrase you need is that Pipex are in Breach of Contract and you demand that they either (a) remedy to your complete satisfaction within a set time (say seven days) or (b) they release you without penalty from the remainder of your contract within the next fourteen days and issue a MAC code.
Write to their head office (not their useless e-mail addresses) and send it via recorded delivery.
Now, to set your expectations. Pipex couldn't find their ar5es with their hands tied behind their backs and an atlas. They will probably ignore your letter or worse still try to fob you off. Stick to your guns, and if they fail to deal with either issue, then write an ultimatum before you involve CISAS. OFCOM also couldn't give a tinker's *^ss for your problems so unless you do things by the book, you will not get any help from the so-called watchdogs and supposed help-sources.
Once Pipex have ignored your letters, you then write again, enclosing an invoice for the wasted time that you have incurred and demanding payment for every month that they hold your line without reason and in breach of contract. I suggest £150 per month as a fair charge. Each month, send an updated invoice. After three months take out a small claims action against them and keep the faith as it were.
Pipex and their spawn are the worst of an increasingly useless and expensive bunch of ne'er do wells. I was with them for a number of years but finally had to take them to court before I finally rid myself of them. They failed to adhere to ONE element of their agreement and even failed to acknowledge the court actions. It took the bailiffs three visits before the issue was finally settled. Anyone reading this: you have been warned!
SHARK!
For every positive action, there's an equal and opposite government plan.