D Mart — While returning an item 2% charge is deducted in case the mode of payment is card

Address:

Mumbai City, Maharashtra, 400027

D Mart is big venture like Big Bazar, More, Food Bazar. Recently I returned an item which I had bought using credit card. To my surprise, they had deducted 2% as it was card charges. But the return amount slip that I signed had the actual return amount and not the deducted price. They maintain a separate register (manual entry) which record the deducted amount.
My complaint is D Mart is not way too small shop to deduct 2% card charges. Secondly they must upgrade their system to reflect the deducted price on the return slip. And also the staff must inform the customers while buying products using card that they will be charged 2% fee in case they return products.