Mamaearth — Cashback not given

I have ordered two shampoo in a cashback offer, I didn't get the cashback later, I sent mail to them no reply for that, then I called them after few months on several try to customer care number.they said the cashback time expired . cashback means I understood as they credit back to my account, atleast they have to mention it will be there in the mamaearth account.even if it is in mamaearth account, how the cash in my account will get expired, if it is any coupon code it will get expired, but how the cash that too without any prior notification.This is again like a scam using fancy words like cashback and finding their own way to loot it from customers.in my order page nothing mentioned as this cash will remain in mamaearth account or will expire in so and so date.so in the name of cash back they are cheating customers.please take action on them in this regard