If OpenAI doesn’t want to make the minimum effort to try to get in touch and get your money in sub-payments, which will ultimately result in the banning of the account, I’d start working up aging on a new account for prepay credits (which will allow more frequent smaller payments).
It is ultimately something that you could have anticipated, and set your monthly limit to no more than you’d have been able to be billed at once when the bill came due.