Car contract

A very bad experience from these guys. My contract with them was supposed to be three years. It reached the end and they continued to take my money. When I called, they told me that I was supposed to send them an email and request cancellation, which I did. Two months after that I get calls from their legal team saying that my account is outstanding! I emailed them the ref number I got for the cancellation, now I am getting calls from different people telling me about the outstanding on my account. I keep on explaining to them the same story I explained to the 1st agent I called.