Customs refund on a lost order

After so many back and forth, I still haven't received my refund for customs on a lost order. Buffalo said that they can not refund the money to me because they do not have a contract with me but with Shein. Shein said Buffalo should do the refund since I made the payment to Buffalo. Buffalo has asked for the refund form and proof of payment more than 3 times but they still don't process the payment.