it won’t let me remove my old card
See -> Remove a payment method from your Apple ID -> Remove a payment method from your Apple ID - Apple Support
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If you can't remove a payment method
If you have subscriptions like iCloud+, have an unpaid balance, or you use purchase sharing, you must keep at least one payment method on file.
even though I got a 50 card put on today
You are talking about Apple Gift Card or App Store & iTunes gift card?
If so see -> What you can buy with your Apple Gift Card or Apple Account balance
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)
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Apple Gift Card and Apple Account balance can't be used for some purchases
- You can't use your Apple Account balance to send gifts or gift cards.
- If you use Family Sharing, your family members can't spend your Apple Account balance. Funds that you add to your Apple Account balance are only available to you. Find out more about how purchases are billed to your Apple Account balance.
Learn more
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See: How to redeem your Apple Gift Card or App Store & iTunes gift card
How to redeem your Apple Gift Card or App Store & iTunes gift card – Apple Support (UK)
When redeeming a gift card, (1) the amount will be credited to your Apple Account balance and (2) then you need to set your Apple Account balance as your default payment.
(1) See -> Check your Apple Account balance -> Check your Apple Account balance – Apple Support (UK)
(2) See -> Add a payment method to your Apple ID -> Add a payment method to your Apple ID – Apple Support (UK)
If you already use your Apple Account balance, the Apple Gift Card or App Store & iTunes gift card is automatically added to your Apple Account balance.
If you update your payment method or add funds to your Apple Account balance, It would take about 1 to 3 business days in order to process.
If you're still unable to update your payment method, Contact Apple Support.
If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)