Incompatible product sold compulsorily

I bought a Tata Docomo computer dongle from Chroma store on Mount Road Chennai, on 11-5-14, on the recommendation of their Chromebook sales man, Mr Selvan. However, after “activation” the device did not work on the computer as it was found incompatible by their own technician. They refused to take back the device and refund the sum of Rs.999/- paid.