I want to upgrade iCloud with apple gift card which I received in email I do not have the physical card

Tried to upgrade iCloud and did not want to use a credit card. Apple suggested an Apple gift card. Received Apple gift card in email. Now Apple won’t redeem the “gift card”. I’m so sick of Apple and all the hoops it makes you go through, just to get ripped off again and again. This 5G phone is the worse!