Sale cancelled after item was already sent

So I made a sale for a pair of margielas on grailed a couple of weeks ago however the sale happened when I was on vacation and way from home and then my area got hit with a snow storm and I was unable to go to the post office eventually I was able to ship after getting a warning from grailed saying I should ship within the next 48 hours 4 hours after I shipped I get an email saying my order is cancelled and my buyer has been refunded even though I already tendered the parcel to ups and had a reciept showing it was scanned

I contacted grailed and they said the tracking number didn’t update which was not true they just spelt it wrong after notifying them of this error they then claim that I dropped it off after my order was cancelled which once again was not true because on the tracking it showed the item was dropped off hours before cancellation

Now I don’t have my item and my buyer isn’t responding even though it was delivered what can I do if anything because they’re not being helpful in the slightest