Refusal of Service already paid for

Location/place: Shop No. 6 & 7, Pacific Mall, Subhash Nagar, New Delhi

Name of company/service: Costa Coffee

Purchased a voucher from Snapdeal.com offering Buy 1 Get 1 Free on all drinks. Staff refused giving false reasons namely, the voucher being valid on other outlets except that particular one. Felt very embarrassed. Came back home & confirmed the outlet from the snapdeal site. Found the staff guilty of inappropriate conduct & reported. Snapdeal Link – http://www.snapdeal.com/deal-delhi-costa-coffee1/?pos=0;0;2
Please take the necessary action as per your sound judgement.