OP, what does 'Have been sent final demand car involved not mine' mean?
The registration number(VRM) is not one for which you are or ever have been the registered keeper?
It's a car which was on hire to you on the date of the alleged breach;
It's a car which was leant to you and which you were driving on the day;
or.....?
And have you received previous correspondence (addressed to you) from the creditor or addressed to another party which they have sent on/given to you?
Probably scopes most of the immediate unknowns!