you can't cancel your auto-debit? Which credit card company is this?

The problem here however would be the T&C. If it is stated there that you are bound to complete one year, then even if you cancel your card, they will still charge you, and later start sending you legal letters stating that you owe them x amount of dollars.

Your best way out would be to immediately write to them to tell them you intend to cancel your membership at the end of the one year period that you signed the agreement for. Keep a copy of the letter and make sure you hand deliver it to them (preferably with acknowledgment of receipt). That would be the only way out, you have to accept the fact that you will loose one entire year of membership fees by signing the agreement with them.

Morale of this is never sign anything without reading the full T&C. There are a lot of organizations out there who do this right now, abusing the unsuspecting users of credit cards. Wouldn't be surprised if there is soon laws regulating the use of auto-debit transactions.