Location/place: chennai

Name of company/service: reliance net connect

i wast told to pay 1500 INR as advance rental pack for 3 months and i did as they told and told no bill will be generated for 3 months. but now they have generated an bill amount of 463 and telling me to pay it before 14th of may or else my connection will be terminated.
(8122545847- form reliance dept) this is the number they called and told to pay 1500 and right now after calling them they said they will change the plan shortly. but nothing happened and now they are not attending my calls..
plz help