Mercari complaint: Mercari’s third party post mate pickup service fid not pickup my package although it is marked that the package was delivered.

Mercari’s third party post mate pickup service fid not pickup my package although it is marked that the package was delivered. Mercari stated that they were unable to reschedule a pickup through their system. As a result I am out of a $295.00 sales purchase. The person expressed that they have had numerous problems with Mercari using post mate and for that reason they didn’t wish to reorder. Also they used a coupon that they wouldn’t be able to use again because of this problem. I have 20 screenshot text messages with Mercari in Reference to this matter and they still haven’t resolved this issue. The customer service rep April asked me to go into the app and attempt to make changes that they should be able and responsible for doing. My item is still marked sold although I haven’t received any money from it due to their error. Mind you Mercari never gave me an option of delivering through the regular mail. Only pickup using post mates third party whom they have no control over if they will actually fulfill picking up packages or not. Mercari should be responsible for paying customers for the sales that were made. If Mercari would have been able to reschedule through their app then I wouldn’t be out of money. I was told that their system wasn’t allowing them to reschedule pickup and that I need to go on the app and do xy and z. I don’t work for Mercari and they don’t allow you to sell for free. So they should be responsible. I am sending a copy of the 6 messages between me and the seller for proof. I have 20 messages more if needed to be provided. Thank you.