Can not do anything on the app store ( need to update my payment method)

Ok, so i got my ipad about a year ago, and for the first three months, i have been using itunes cards to download stuff from the app store. Soon after this, i realised that since i dont really go out, it could be a bit of an inconvenience for me, so i decided to use my debit card instead. Things were great, until i reslised i had no money left on my account, which apple notifies you of by saying "your payment method has been declined". At first i was confused, but after trying to buy things from amazon and steam and getting the same error, i realised that i had no money. This is where the problem began. The fact that i couldnt buy apps didn't bother me, but what DID bother me was the fact that i couldn't update my apps, download free apps or even install apps i have already payed for without getting that **** error message. This lasted for a little while before i got more money on my account and it worked again. But that isn't the end of the story, about a week ago, i could no longer do anything on the app store without getting that error, EVENTHOUGH i have money on my account. I knew this because right after that error messaged popped up for the trillionth time, i brought a book from amazon with absolutely NO PROBLEMS.

I am so irritated. Fix this apple!