They have been billing me for 16 months over contract period

I took out an extended warranty in June 2014 through my financier Absa, I was supposed to pay a premium for 24 months as per the contract, 40 months later they are still debiting my account. I can not stop the debit because its combined with my car installment. i have call them numerous times to stop the debit and to get a refund for the 16 months i have been debited with no luck. Every time i call i get told that my matter has been escalated but i cant even get a reference number or confirmation in writing that my matter is being attended to.