Unable to remove credit card from Apple Music subscription with gift card

I haded to cancel subscription to be Able to remove my credit card I didn’t think I was going to cancel my Apple Music to because i pay with a gift card not with my credit card ..? What can I dot with that and o ready lost the paper that haded the code of the gift card I don’t know why it did that if it supposed to be 4 months

[Re-Titled by Moderator]