Ridiculous Amount Charged after contract cancelled

After a 24 month contract I cancelled my contract per email. - December 2014. According to them they did not received the email. My contract went on resulting in arrears. Between Jan and April 2015 they suspended my services. After numerous phone calls by me I had to pay an outstanding balance of about R500 before they converted the service to prepaid. Suddenly in Jan 2016 I'm being threatened by lawyers for an outstanding balance of R939.32. THEY MUST GO BACK TO THEIR RECORDED PHONE CALLS!!!!!!