if there is a policy, then there has to be a record in the insurance company. Could it be that you have changed name (married/seperated/divorced) since you took it out, or that you put another name (partner/spouse) onto it since you took it out?
In any case, they should be able to get it by address.
Are you sure that the payment being take out is for house insurance? Could it be for some other type of insurance?
Have you a broker - if so, he should be able to trace it
Have you a mortgage - then the lender should have a note of the policy number