Heritage Foods Limited — cheated public with their offer

Website:

www.Heritagefoods.in

Sir, the problem is with the offer given by heritage in association with paytm.. I have bought heritage badam flavoured milk which costs ₹25 and it is there that ₹10paytm voucher.. The product manufacturing date is 14aug2018,, i tried to apply the code in paytm,, it is showing "offer not active". I referred its t&c, it was there that the offer is from may to 20th june2018,,. So my question is that if the offer ends by 20th june2018, how heritage company printed about the cashback which was manufactured on 14aug2018??
Because of the same i had to pay an extra amount of ₹500 for believing that incorrect offer..

I already sent an email regarding this but their team responded carelessly and nothing happened, i have been cheated and provided nothing..