Get the head honcho's name (Edward Troup?) and the HMRC address, for PAYE and self-assessment, which sounds like the department you are dealing with, it is:
HM Revenue and Customs
Pay As You Earn and Self Assessment
BX9 1AS
United Kingdom
Now, sit down and very calmly write out the most strongly worded complaint you have ever composed. Tell Mr Troup that if you do not receive written confirmation that the issue is resolved, within 14 days, you will cc into an original copy your MP, the BBC, Sky, Daily Mail and the F.T..
You then place the letter in an envelope on which you have written: "If you are not the person named on the outer envelope you have carried out the criminal offence of tampering with mail, which could see you liable to a prison sentence. I now request that you deliver this envelope, unopened, to its intended recipient."
You then stick that in a named and addressed envelope and send it recorded delivery.
It might not have any real basis in law, but it sure makes them sit up. I got a hand written reply on HoC letter paper from the second in command of the person I was having my war with.
about 10C more than is normal for this time of year 
