How do i get itunes to accept my debit card. When i fist made my account everything was fine but after a few purchases it was declined, i have money in my account so i do not know why it would have been declined. My bankacount says it should go through?

I set up everything with no problems the first time. I have money in my account and i made a few purchases though the app store, then all the sudden it says my card is declined... but i havemoney in my account, it makes me try to change my billing informaton. I contacted my bank and they said there is no reason that my card should be getting declined. I cannot download anything, or update the downloads that i already have... this is so fusturating, any ideas to fix this.