1. Contact the online course website or seller: First try to contact the online course website or seller, explain your problem and ask for a refund or solution. If the seller is a legitimate business, they may cooperate with you to solve any problems and pay you back.

2. Submit disputes: If online payment methods such as PayPal are used, you can try to submit disputes on the platform. These platforms usually investigate and try to solve problems and try to ensure that your rights and interests are protected.

3. Contact the bank: If you pay by credit card or debit card, you can contact the bank and ask to cancel the transaction or make improper statements. They may also help you get a refund and prevent future fraud.

4. Report to the local consumer protection agency: If you can't find help on the website or fail in any other way, you can report the problem to the local consumer protection agency and ask for help. They may provide legal advice to help you solve the problem.