Sangeetha Mobiles — cash back not received after 120 days

Address:	560102
Website:	Cash back not received

I had purchased a New Iphone 6 32 GB Space Grey - Apple with IMA number [protected] on 12 Feb 2018 from Sarjapur branch Bangalore - Invoice number - SI/SAR/2909 for INR 26, 990 with an ongoing offer of INR 7000 as cash back. I paid for the phone via my HDFC credit card. However, I am yet to receive the cash back which was due 90 days from the date of purchase.

I have already checked with my bank and they have confirmed that they have not received the cash back and asked me to contact the merchant.
I have spoken to the merchant multiple times but my problem is yet to be solved. Please note that the cash back was due by 12-13 May 2018. I have been on mails with the Sangeetha Mobiles customer care for the past 15 days but they said that if you do not have the charge slip we cannot do anything. I told them that i had lost the charge slip but have the invoice and asked them to share the transaction id by which they would have processed the other cash backs. But they just kept on avoiding the issue. They are harassing the customer and do not even have a helping attitude. Plus when I call them they avoid calls. Its a cash back for 7000. Can any of you help me here?