Diamond Membership not applied
You haven't lost any days. Your subscription starts when Billing activates it and it's not an automatic process when you buy from an app store. Usually a week or so; I know it sucks to have to wait, but they're very busy with Holiday giving and all the Beth Harmon inspired new members.
With the holidays and increases in tickets, the billing staff are a little behind. They will get you handled and should be able to fix any issues with timing. It may take a little longer to resolve due to that.
If you're on the app have you logged out of it since you upgraded? If not, log out and back in.
Have you opened a ticket with support?
https://chesscom-support.paperform.co/
I'm not aware of any payment issues in general to be fixed
I suggest that calming down and waiting for a reply from support is your best option.
Without getting into it , it looks like there was a complication with your old account.
If you need help, please contact our Help and Support team.