apple failing my cvv on my debit card

this happened when i first got my phone last year september. my cvv was failing on my apple payment method for some reason, i managed to fix it last year and now it’s not working again. this has been going on for a month now and it’s really annoying me as i have no way of fixing it as i’ve tried and searched everything. does anyone know how to fix this problem ?? also this issue has stopped me from installing apps too, it just asks me for my card info and declines it then i can’t get the app !!