I have serious problems with the payment type. I always use a prepaid Visa card but the late days I can't buy anything because the card is now unacceptable! Can you please help me?

The iTunes Store typically does not take prepaid "credit" cards since they normally have no billing address associated against which to verify. Why the card worked before but not now I don't know, though Apple has been tightening up their security and that may have finally caught up with that card. You can try contacting the iTunes Store and asking if there is any way to use your card, but they may just tell you that it's not possible.

http://www.apple.com/emea/support/itunes/contact.html

If it is not, then you will need to use a true credit card or purchase prepaid ITunes cards, if Apple has issued them in your country.

Regards.