Consumer Redressal

I bought Panasonic Eluga A mobile handset from PayTM Website for Rs 8,085/- on 15-October-2014 , which due to some problem in the Mobile purchased, as per their return policy ,was sent back through their registered Courier Agency (they picked from my mailing address) on 28-Oct-2014 , till then i have not received my refund of balance amount for Rs 6,468 /- by deducting their promotional cash back of Rs 1617/- (already utilized by me). Number of mails have been sent to them but no favourable response being received from them nor they are sending any confirmation related to refund of my money. Request help on priority as my Credit Card company has already charged me for late payment fee, interest and EMI also.