I've had my Maestro Card for around twelve years now, and never had any problems with it. Until last week, when I tried to pay for Broadband and they wouldn't accept it. What's going on?
Have you phoned your bank and asked. They should be able to see any transactions, authorised or declined and be able to tell you why.
Has it worked since?
Maestro is Mastercard's debit card. Mastercard insist that any online retailer must use mastercard safesure and a lot of them have refused to set it up and no longer accept the card. You can still get Maestro cards but most of the big banks have switched to visa debit cards which until recently gave customers more protection.