Paytm — Refund Rejected by paytm

I ordered a Apple Watch series 3 and the size I was expecting was not same. It did not fit me so I requested for an exchange or refund but Paytm refused my request. This is my first time shopping from Paytm and I am very disappointed. I did not expect such behaviour from them. Their customer care is also unreachable. I am not able to talk to them. I want refund or exchange of my order.