Consumer Redressal

Dear Sir/madam, I\'ve taken a post paid data connection(9143062640) from MTS,almost 3 yrs back. During this period I\'ve paid bill without being defaulter. On 24th/25th Mar\'14 I\'ve requested their cust\'care to change my bill plan from 555 4GB to 550 3GB unlimited.The cust\'care told me that the new billing plan will be effective from 1st April\'14. On 1st April they told me that \"you it would take another 7 days to activate; I called them on 6th, as the billing plan was not changed & I made a complain. Their cust\'care executive told me that I should keep using the service the billing plan has changed. On May they send me a bill of Rs. 1762 which was suppose to be around Rs. 650 as per my new bill plan. I again called them & made a complain;the cust\'care executive told me that I would get a \"Waiver\"; but no one respond even after 10 days. I again called & made a complain. Now they are offering waiver Rs. 300 & asked for bill payment without that they will issue legal notice.Kindly suggest