1. Friendly communication: First, carefully check the credit card bill to find out whether the cardholder has any outstanding money. If there is any outstanding money, you can contact the bank for friendly communication to find out whether there are any problems or mistakes.

2. Contact customer service: If there are bad debts in the bill, you can contact credit card customer service to find out the reasons and solutions.

3. Submit an application: If the customer service can't solve the problem, you can submit an application and ask the bank to investigate and handle the bad debts.

4. Waiting for the investigation result: After submitting the application, you need to wait for the investigation result of the bank. If the bank thinks that the bad debt is the cardholder's responsibility, the cardholder needs to provide relevant evidence to support his claim.

5. Processing result: If the bank thinks that bad debts are the responsibility of the cardholder, the cardholder needs to provide relevant evidence to support his claim; if the bank thinks that bad debts are the responsibility of the bank, the bank needs to provide relevant evidence to support his claim; if the bank cannot determine the cause of bad debts, both parties need to negotiate a solution.