Contact the buyer directly OR
Contact the customer support team of the platform where you sold the item. Explain the situation to customer support and ask them to help you recover your payment. Customer support may be able to contact the buyer on your behalf or help you to file a dispute
Here are some tips for recovering payment from a buyer who has canceled an order without your consent:
Be prompt and professional in your communications with the buyer and customer support.
Keep detailed records of all communications and transactions.
Gather any evidence that you have completed the requirements of the order, such as screenshots, emails, and tracking numbers.
Be prepared to file a chargeback or take legal action if necessary.