How can Dr. Rainbow complain if he doesn't get a refund?

Complain to relevant regulatory authorities.

If Dr. Rainbow refuses to refund, he can complain to the industrial and commercial bureau, consumer associations and other institutions. Provide relevant evidence such as purchase contract, payment voucher and refund agreement to support the complaint, and ask the regulatory authorities to investigate and take corresponding measures to protect the rights and interests of consumers. The organization will supervise Dr. Rainbow's business activities and help solve the refund problem to ensure that the rights and interests are protected.