Shoppers Stop — 15% cashback offer couldn't be availed

Address:

Kolkata, West Bengal, 700014

I had received a text with the offer of 15%cashback if paid via paytm on purchases above rs.6000/-. Yesterday my total bill amount crossed the required rs. 6000/- but the billing counter couldn't take the payment via paytm so i didn't get the cashback offer. If the offer is not being available i think customers should b informed. How do i get my 15% cashback now?