Despite submitting an application to deactivate the connection, monthly bill being generated every month

Location/place: Bangalore

Name of company/service: Tata Teleservices

I had bought a USB Internet device from Tata Docomo and had requested for a post paid unlimited plan. After using the device for a couple of months I no longer needed it, and therefore requested them to deactivate the connection. I called up the customer care for the same and I was told that I can keep the connection is safe custody for 3 months at a charge of Rs. 300/-. I declined their offer on which the CCE told me that as a special case they would even waive off the charge of Rs. 300/-.
To my surprise I get a bill of Rs 300/- after 3 months. After call the Customer Care I am told that none of their CCEs could have suggested a free Safe Custody. I insist on immediate deactivation to which I am told that I will have to come to their office in person and to a specific office which was approximately 25 Kms away from my house.
I did not pay the amount instantly expecting them to withdraw the connection but to my surprise they kept on billing me for 2 continuous months even after non payment and did not withdraw the connection. I personally went to their office paid the amount and gave a application to deactivate then and there. I was told that the connection have been deactivated.
Now after 3 months I again receive a bill of Rs. 326 and I am asked to pay immediately to enjoy uninterrupted services