Impossible to cancel contract

I sold my car on the 17th of August.I then immediately called car tracks call centre to cancel my contract. However I could not get through and then started a chat on their web chat facility where I was provided with the form to complete as well as the email address to send the form to. Which I did. On the 17th of August. I got absolutely no response from them until last week. The email I received last week kindly informed me what my options were and that I need to give 20 days notice. The problem with this is that I have already done this on the 17t of August. I rep**** to the email stating that I have already completed the form and I also forwarded the previous email. But again I received no response. Today I sent an email to ***, the email provided on their website if you are not happy with their Customer Care service....and again. No response