Netmeds — Cashback not received

My order minimum amount was 1264.77
It was my first order
The offer was 25% off on medicine and 50% cashback as nms wallet amount.
The offer got applied and the discount was 311.23(25%) now the medicine got delivered but no cashback. Now on complaining they said the minimum order amount after discount should be 999 and mine was 953 so not applicable.
My question is then why did the offer get applied in the first place ? Isn't this false advertising and cheating?