Mercari complaint: Breach of Contract By Mercari

On July 3rd I sold a Kate Spade wallet for $55 on the Mercari platform and dropped it off at my local post office on July 6th. Unfortunately USPS messed up and lost the package prior to scanning it in so when it had not began tracking by July 18 the buyer was able to cancel the order and receive a refund. On August 12th the buyer contacted me letting me know they received the item. When I checked the USPS tracking it showed the package was scanned in August 6th an hour away from where I dropped it off. Mercari customer service told the buyer she could just keep the item since she had already been refunded but when I asked about receiving my payment they denied my request because I “shipped the item after the order was cancelled therefore I am not eligible.” According to Mercari’s policies if an order is delivered after being cancelled and the tracking shows delivered or the buyer s receipt of the package the seller qualifies for a payment if:
1. The transaction was cancelled by the buyer or Mercari.
2. The seller ed they shipped the order by tapping “” on Mercari.
3. The seller has not already been reimbursed through Mercari shipping protection for the item.

I fulfilled every requirement under their policy but they still refuse to approve my request. This is a Breach of Contract.