Apple doesn't usually accept prepaid debit cards.
Contact iTunes or Mac App Store Support to get help with your account.
Mac App Store Support -
http://www.apple.com/support/mac/app-store/
iTunes Support -
http://www.apple.com/support/itunes/
Late 2012 Mac mini, OS X El Capitan 10.11.3; Apple Watch, 38 mm silver AL, Watch OS 2.1; iPad Air 2 & iPhone 6+, iOS 9.3