debit card failing in app-store??

recently, i’ve been trying to update or download apps and the app-store wont let let because its saying that i have a failed debit card. i would try and update an app like instagram, for example, and it would tell me to sign in through my apple account and then tell me re-enter my card information. once i do that though, it repeats the same process over again. i’ve tried to contact apple via email and they haven’t responded thus far. what should i do?