Myntra.com — Serial number not match when return pickup

Address: Champhai,Mizoram

I have ordered H&M derby shoes from myntra and the size are large as usual size, so I return them and when the delivery guy came the serial number mismatch the system.So I called myntra customer care and they told me to wait for 48 hours and after that I received a message saying that my queries have been solved, but my problems are not solved because they cancel my return request, I called them many times and they always said to me to wait for 48 hours, please help me fix my problems