Harrasement by Shriram City Union Finance Ltd?

I had bought a Television thru Shriram City Union Finance Ltd in August 2005. I had been a very prompt payer and have cleared all the EMI's without any cheque bounces on time. Last week; they have sent me a Notice asking me to clear my due Rs. 2675.00. I have my bank statement showing the clearance of all the 8 cheques that i had issued. I am deeply disappointed with the choice of words used in the notice and when i called them; they have absolutely no phone ethics while talking to their customers. One moron calling himself as an advocate from their legal department hung up on the call without giving any info. I would like to go in a legal way to stop such harrasements to public by these people who dont probe into their records and start shooting nasty letters. Pls guide how do i take them legal?