Closed Acc 15 Monts ago but billed for it

I closed my DSTV acc 15 months ago and confirmed account paid up. I even received a email asking me to complete form as to why i closed acc. On Friday i was phoned by DSTV accounts dep and told i owe 15 months payments and that my service is now suspended. (a service i did not have). I told the lady i would not pay and they were at fault. An hour later i phoned call centre and was told i did owe money on their system. After explaining Lady spoke to supervisor and told me the complaint was being bumped up as she could see up till May 2014 account paid every month and from June 2014 my decoder was not connected. She told me the acc dep would contact me on Friday but till now no response at all. I tried to email a complaint directly to Multichoice but if you don't have acc number you can not!!. This i don't have as i closed my acc over a year ago. Plus what company will let you receive a service for 15 months without payment.