Definitely sounds like a bug. The rate should be quickly unlocked after they receive a payment. Check to see that you got the actual charge on your bank or charge card billing, because I inferred from another post that the payment processing and application to an account may be queued.
Generate a new API key and see that in use it picks up on the rate shown there.
If they took your money and still don’t let you spend it quickly, you can contact with a message about your account configuration problem via the help.openai.com assistant.
Also note that GPT-4 can seem like it has a request-per-minute rate limit, but it is actually from the tokens-per-minute. It can’t produce as fast as the limit if it’s just you, but if you put a big document in chat history and start talking about it, resending the input again can burn through the allowed tokens.