Reliance Communications — Not cancelled when requested

Address:	560014
Website:	reliance.com

Hello.
My Reliance post paid data card no [protected], which was terminated as it was migrated to 4G, 2 months prior to this happened i had requested for the services to be cancelled as the internet was not at its best. i made several calls to reliance customer care who kept saying that this will be resolved which was never done till the last date. but they continued charging me the monthly rental.
during the last month before reliance was going to migrate to 4g they called me to buy a new data card which was going to cost me nearly 3000, but i was not prepared to do this & asked to cancel my services asap. had a tough conversation with one of the agents in the call center he said i will not be billed anymore as i am up to date with my bills so i stopped using the dongle as i already had my new provider active at home. the dongle was automatically terminated. but there after i have had lot calls from reliance asking me to pay the final bill. initially they said its 2 months bill & it is 1400. i should be paying no more for that subscription. due to the fact that i was up to date. & it was never my mistake.
now they say that it was their mistake that they said the amount is 1400 but it is 670.
they have passed to people in delhi who keep calling so many times a day & using abusive language.
one thing i have understood is that i should have no more services from reliance. i have another reliance postpaid number which i am looking to cancel & they keep saying that i have to go to nearest reliance outlet which i did, but the people in the outlet also say they cannot cancel it.. what should i do. is this my mistake?
please help me with all this.