Zomato — misleading cart value

Address:

Howrah, West Bengal, 711204

I placed an order with zomato at domino's pizza on seeing that it was offering discounts on that restaurant's order. My cart value was rs 248 before applying promo code, and after applying the promo code the price became rs 153.6. The final amount shown was rs 153.6 and placed my order through paytm only to see that my account was deducted by rs 248.
On having a conversation with zomato's support, they said that they can't help because it was a technical glitch.
Since it was a glitch on zomato's part, then why should we consumers face monetarily. Zomato is misleading the customers to place an order with it.