http://www.seagullstickets.com/screenloader.aspx?page=documents/html/tandc.html
terms and conditions for season tickets load fine for me on the above link.
If you cancel the direct debit with you bank then the club are likely to take legal action to recover the money, or sell the debt to a collection agency who will try to recover it from you. I'd also think they'd put you on a black list so getting tickets in your own name anytime soon would be...