UniverCell Mobile — Misused my Credit Card

Address:

Bangalore, Karnataka

I have purchased HTC Explorer mobile from Univercell Indiranagar (Bangalore) branch (21-July-2012), and I used my credit card for EMI payment.
When my credit card bill came, there were two purchases has been deducted. One was my mobile EMI and one more EMI of some others' purchase.
They miss used my card to pay some other person's purchase. I remember, one lady was quarreling with payment department about money when I was waiting for my payment. I doubt, for that payment payment guy purposefully used my card.

I enquired with them along with my credit card bill statement , and asked for the receipt of extra payment in my credit card. They failed to give the receipt with my signature which generated during swiping.