My mobile phone number has been used for 9 years, so it should be a second-hand number. The original owner filled out all the credit cards he applied for last year with my number, and most of them have been debt collectors recently!

This should not happen. Because now it’s a real-name system. A verification code will be required when applying for the main number. If your number is with you, he will not receive the verification code and cannot keep yours, unless he leaves a backup number. The number of a relative or friend is yours. Then this is no big deal. Another possibility is that there is a problem with your own credit card and it is overdrawn by someone else. You will definitely be pressed for repayment. I advise you to go to the service hall for consultation, or log out or block the other party, or directly tell him that he made a wrong call and stop harassing you in the future.