Falsely reporting your card as "comrpomised" is a hassle for you and for the issuer and may carry consequences. Moreover, merchant vendors who supply recurring services are simply supplied the new card number (big difference between closing an account and issuing a physical card with a new number).

All you need to do is follow the cancellation process set forth in your contract with Experian. If it requires a letter, send a letter. If a call will do, make a call. You no longer owe further payments and as it is a prepaid service, you do not have any delinquencies. You also have an easy chargeback should Experian continue to bill you.

It's just a matter of following the specifics of the contract which you agreed to.

This also brings up the simple point that it makes sense to read these contracts before you sign up. It always seems easy and cheap, but if isn't.