UniverCell Telecommunications — Paytm payback not working

Address:

Chennai, Tamil Nadu

I bought the samsung e7 mobile on feb 28, 2015 in univercell and they gave ptm cash back offer about rs. 3000. When they provide first time itself i started to face issues with the offer.
First issues were its not correctly activated on time. Daily i walked in to stores and then they activated. After that i used only one time alone. I missed to convert the paytm code into amount (Didn’t added the money into my wallet) . Actually they told me to use that offer every month or within 6 months i can able to use any time, so i tested one time and its worked. After that i planned to use in single time at last of month of offer.

But now they are saying i can’t use this offer without adding the amount into my paytm wallet every month and they are not responsible for these issues. And they are saying i need to fight with paytm and get the amount.
Is this the way to treat the customers?