Paytm - Overcharging of MDR charge on credit card using PoS machine

Paytm company told me that they will charge *.**% charge on credit cards payment through PoS machine and today on * december **** I swiped a credit card and they are charging *.**% MDR charge on that payment and now I am asking them to refund so they are making an excuse by telling that it was different type of card , you should have charged it from the customer, they never told me that there is any such charge of *.**% , neither it is showing on my PoS device. I have proof too I have taken photo graph of MDR charge and actual charge taken by the company. Please help me as this is a very serious matter.