It will not accept my payment method Change. I lost my card and need to change to a new card

Check the following

1. The payment method that you are adding is of the same country as that of App Store Country on your iPhone
2. You have valid payment plan / debit / credit card from an authorised bank from the same country
3. Payment methods that you can use with your Apple ID - Apple Support
4. Learn more about family purchases and payments.
5. Please check if your Debit/Credit card is valid internationally

Did you try entering the new card before removing the old card? Also, it would be helpful if you explained in detail exactly what is going on.