Paytm Mobile Solutions — promo code not applied while concluding the bill

I tempted by an advertisement in dna news paper published by you stating that festival sale by paytm mart which was offering about 60% cash back on purchase of more than 10 articles of daily need goods. Accordingly i ordered 16 articles amounting rs. 3634/- by order no. [protected] dated 5/10/2017. At the time purchase of each article i had selected promo code and the system was showing the discounted price. I booked the articles and paid the money with the expectation of 60% cashback. On 11/10/2017 all the articles were received there was no sign of cash back. I lodged a complaint for cashback. Then i came to know on 14/10/2017, i was supposed to apply a promo code while concluding transaction again, so i was not done that so the cash back was not offered. Their message dated 14/10/2017 further stated that as a goodwill gesture, they are adding rs. 54+120+74+74+74 totaling rs.396/- to my paytm wallet as cash back as per the prevailing code stealdeals 40 on 5 products.

In response i wrote on 15/10/2017 and declined your offer of rs.396/- cash back which is about 11% of the order value instead of promised 60% cashback and requested for cashback as assured. Further i called their customer care on the same day and discussed the matter, their representative was repeatedly reading the same message of 14/10/2017. When i said i am not satisfied with his offer and stereotyped answers and asked for escalation. For that your representative stated that his senior will also offer the same thing. There is nothing they could offer more and they cannot apply same promo as on the date of my order. Then i insisted him to write to me what he was stating. He said he cannot. When i insisted i wanted to escalate the matter, he said i may have to wait for long i. E., may be 15-20 minutes and when i asked him arrange a call back from his senior, he declined for the same.

Considering my whole experience from start of order till now, there are certain questions unanswered, which i requested them reply point-wise.
Why there was no alert to include promo code manually when concluding the purchase, whereas at purchase of every article system was prompting to select promo code. Which i did religiously to understand price. It is deliberate attempt to deny the cash back and it seems false promise and as stated by their representative that many people forget to include the promo code. Is this the trick to help the company show something big offered and deny the customer what he is promised by picking up the technical trick?
Why there is no escalation by your customer representative?
Why largess of 11% as against promised 60%?
Then i wrote to them in case they believe their customer service is best and as stated by them, if it is good will gesture, i deny the offer and i requested them to either credit cash back as promised and what i rightfully deserve or else take back the cashback of rs. 396/- credited by them.

There is no response even after escalation. You can not write to them through mail and you can only write through app or website and they closed my two complaints without answering.

I am very regular online purchaser. This is my worst online shopping experience ever.