Consumer Redressal

I purchased a MTS Ultra 3G dongal in the month of April in which i was promised to get 40GB data at high speed upto 9.8 MBPS @ Rs999 p.m. & in the begining it worked fine. However after 15 days,speed became slow & went as low as 200 KBPS. When I contacted customer care they said that my area is a poor coverage area hence they can not provide speed more than 200 kbps. Then I contacted Appellate MTS Delhi & got even worse response. When I asked appellate to solve my issue & if can not resolve then refund my money, they straight away cancelled my account and when I asked them about cancellation request then they revoked that however put my a/c in no payment. Now my concern is if my area of residence is poor coverage zone then 1. Why I was offered the dongal on confirmation that it will work perfect 2. how come dongal worked fine for initial 15 days 3. What would I do with the dongal worth Rs 1500 4. For what service I would pay Rs1000 pm Hence please advice how can I take legal action.