Refusal to refund contribution overdeducted

At the beginning of December 2014, I terminated my Discovery health and vitality membership with effect from 31 December 2014 - membership certificate was issued to this effect confirming the cancellation. To my surprise Discovery Health still deducted membership fees from me in January 2015. on the 16 January 2015 I called requesting the refund (I was told the request has been send to billing specialist to refund me), nothing happened. On the 2nd February 2015 I made a follow up and was requested to send proof that I was not getting any employer subsidy - I emailed my payslip to and receipt of it was confirmed and I was promised that I will receive the refund in 7 days, to date still nothing happened. On the same day (2 Feb 2015 - I logged a call to their internal complaint (Ref No ***), to date no one has responded to my complain. I called again on the 9 Feb 2015 making a follow up on the refund, I was told that the billing specialist says they cannot refund me. To date I still have not been refunded both the membership fees and there's no light that I will ever be refunded whilst the company is *******ly keeping my money and earning interest on it.