The rules in relation to the use of Bills of Sale are clear and state that the bill of sale must be registered within 7 days of signing both the consumer credit agreement and the bill of sale document, otherwise the debt is unenforceable. I would suggest you take your documents to your local Trading Standards Dept, or take the matter to the small claims court for resolution. If the bill of sale has not been processed correctly and is not witnessed by an independant individual (a person not a party to the contract) it can not be enforced I have seen the MM documents and they are flaued but you will need a county court judge to make a judgement for you.

Bills of Sale must be registered with the Courts of Justice within 7 days of signing the bill otherwise the bill is unenforceable.