Hi Sezzika, send the letter to the same address Pipex ask you to write into for all correspondence (I don't have Ben Sims' letter with me at the moment - sorry). I actually sent my last letter to Peter Dubens, Chairman, at his home address and he must have passed it on to Ben Sims for me. Send it recorded delivery in any case. If you wish to rescind your contract (which legally you should be able to) tell him this. Don't ask him, simply state that you wish to cancel your contract because of the X, Y & Z and you also request a Mac Code.
Good luck. (PS) I cannot find any good reviews about any ISPs. They are all bad in one way or another. I have until the end of November to switch to another provider otherwise my Mac Code from Pipex will be useless, but I'm having real trouble finding a decent ISP. I was going to opt for AOL, but a friend of mine, who knows a lot about stuff like this, told me to forget AOL because they have over-subscribed and provide poor service as a result. He recommended BT, but I'm not sure about them because they want to tie you into an 18 month contract. I noted that Virgin do not have any minimum contract, so I may opt for this company. I wouldn't like to be tied into another 12 month minimum contract, not get the full package/support again and have to spend loads of time writing letters.
Let me know how you get on. If you would any help in the drafting of your letter to Ben Sims, you can e-mail me directly, but I will wait to hear from you first. Kind regards, Sara.