Reliance Communications — False commitment against selling pro3 datacard

I had taken reliance data card 4G connection, named as pro3, which is a post paid connection. I had purchased on 05.03.15, after installation the speed of the data card is only 20-30 Kbps. I have given several companies, mails, against the same, but till now I didn't get any services from them. Every month they are generating the bill for an amount 999+ service tax, and not even change the plan and package. Please help me to get rid of it. I just want to disconnect the connection which I had taken. Kindly help...