Cheating with Dominos coupons in Technopark outlet. Review on Domino's Pizza, Techno Park, Trivandrum

This is based on the incident my brother had with the  Dominos Pizza counter in Thejaswini building Technopark Trivandrum. As part of the redeeming rewards points in my dad's credit card, we got a gift voucher worth Rs 400 from Dominos. Last week my brother went to the Dominos counter with these coupons. They gave these conditions. If the value of the product is less than the coupon they will not give the balance. Well I do understand that as when u redeem coupons it generally happens that way. But the next condition they said was completely absurd and we can call it cheating. If the value of the product is more than the coupon they will not accept the differential amount in cash. I have redeemed many coupons and not once I had encountered such a rule. So my brother who was planning to buy a pizza of Rs 112 decided to buy a pizza of 180 as he had only coupons of Rs 100 with him. So in effect they not only made a customer to unnecessary buy a costly product also they made a cheating of Rs 20. Never accept dominos coupons or any other offer from them. Already their products are over priced. We don't need to give them additional profit with their cheating ways.