British Gas demanding money I don't owe!

theloser_2

British Gas recently sent me a letter demanding the return of their money, £277.42, which they (allegedly) sent to me as a cheque. they claim that the cheque has definitely been sent and that is has been cashed. They claim that it was cashed 28.7.07 but cannot tell me WHERE it was cashed because someone didn't fill in that field on their system. I have asked them to find the archived cheque so we all can see where it was cashed but so far they have refused to do this (I believe the cheque does not, and never did, actually exist!)
I have explained my problem to four different "advisors" so far, tried to speak to supervisors (always in meetings) and asked to speak with accounts section but I can only ever get as far as the advisor level and all THEY keep repeating is "the cheque has been cashed so you owe us the money".
I can produce bank statements for the relevent period showing that this cheque has not gone through my accounts.
I can't afford a Lawyer and I earn too much to be eligable for legal aid, can anyone help or advise please??????
David