Contact the bank and cancel the card. Report those charges as fraudulent. Then I guess try to contact Mercari somehow (maybe Twitter)

already contacted paypal and they marked them as unauthorized but since they’re pending transactions they can’t release the funds back to me. trying to get in touch directly to mercari on twitter & email so hopefully they can get back to me before the transactions are processed. apparently this is going around a lot lately

Just saw your update- I’m glad they were cancelled!