Sorry I cannot see what the actual problem is. May you please describe it again?
Did you check the Google Payment outside of Stadia? It is linked to the same billing account.
Nevertheless billing / payment is a sensitive context. You might want to chat with the support directly to avoid leaking information or to speed up a solution finding.
https://support.google.com/stadia/contact/stadia_chat
Good luck!
Did you ever get this solved? I have the exact same problem and support was unable to help.