Mercari complaint: Mercari approved a cancel order request for no good reason

Buyer contacted me with an Offer of $225 on my $300 beautyhair care product, valued at $390. I accepted the Offer within hours, and answered some questions. I shipped the same day. Days later I noticed that the day after I shipped, A request to cancel the order came from the buyer. I responded that the product had already shipped. I received dozens more buyer messages over the week following. Because I was in the middle of a cross-country move I didn’t see all of the messages until many days later. The buyer demanded a forwarding address. I did not have one at the time because our apartment in Sedona, AZ fell through and we were in the midst of scrambling to find a local apartment that would accept 3 dogs. Mercari okayed the return without any explanation the product has been shipped to my P.O. Box with only 13 of the product in the bottle.