Mts — MTS wi-fi modem not working in windows 8.1

Address:

Thanjavur, Tamil Nadu

I bought this modem only after confirming that it is supported in windows 8.1. (Mentioned in the back cover). But now it is not working in my system and when i contacted the customer care, they said that they are having problem in 8.1 OS and asked me to change my OS. I don't wanna change my operating system and i need either a solution for my problem or a refund for my product. Where should i complain for this issue??