Mercari APP for Smartphones Stole Money and Product Texas Internet

 I recently Downloaded the Mercari Buy and Sell App on my iPhone. I listed a few items to sell and a buyer had purchased a product I was selling. I chose the option to ship the item out myself. It cost me 13 dollars to ship this item out to Texas to the buyer. I was in constant communication with the buyer to let her know that the item would be arriving at her location on June 29th. I had also told her if there were ANY problems with the tracking number provided to contact me right away as I still have the receipt saved from when I sent it out. A few days after the transaction took place I received a notification the transaction was canceled because the buyer claimed she "never received the product and I never shipped it to her" That was on June 25/26. She notified Mercari and instead of COMMUNICATING with the seller they canceled the transaction and refunded her money back. I went back and forth with the buyer who claimed "she communicated with me but I never responded" she also stated "she never received the product and that I was fraudelant and never sent it" Again this was between June 25-27. I stated to her numerous times the product should be arriving June 29 and if there was a problem with the tracking number she should of communicated with me and I would of looked over the receipt from the post office. She then threatened to not send the product back when it did come in. She also stated she "went out and bought the product elsewhere" She lied to Mercari about not receiving the item to get a refund because she "bought the product cheaper at Walgreens" I contacted Mercari with the information I had and they keep responding with "we are working with the buyer to get your item sent back to you" Instead of contacting me before canceling the transaction they just canceled it and refunded her money back. HANDLED completely all wrong. Mercari is refusing to reimburse my money for the product and the $13 dollars I wasted to send this product out to a deceitful buyer. In fact their customer support is a joke. You can't speak to a real person. It's basically a chat session back and forth through the APP. Due to mercaris lack of professionalism in contacting me in the event there could of been a problem with tracking info that I could of easily corrected if they communicated with me before canceling the transaction, I am now out $13 for shipping this product and lost the product in general bc the deceitful buyer is refusing to send the product back. Mercari is refusing to refund me anything but did not hesitate to refund HER money back without even contacting me about the transaction. They are unprofessional and lack integrity as a business. I do not recommend anyone to sell products through their website.