I suggest you go to court to sue the other party for breach of contract, double indemnity. Remember to prepare your contract as a fitness card and the evidence of how long he promised to use it at that time, such as leaflets, receipts and so on.

by law

Consumer rights law

Article 49 Where a business operator commits fraudulent acts in providing commodities or services, it shall increase the compensation for the losses it has suffered according to the requirements of consumers, and the amount of the increase in compensation shall be twice the price of the commodities purchased by consumers or the cost of receiving services.

law of contract

Article 107 If a party fails to perform its contractual obligations or fails to perform the contractual obligations in conformity with the contract, it shall be liable for breach of contract such as continuing to perform, taking remedial measures or compensating for losses.

Article 108 If a party expressly expresses or shows by his own behavior that he will not perform his contractual obligations, the other party may require him to bear the liability for breach of contract before the expiration of the performance period.