Refusal to acknowledge cancellation of medical aid

I have been a member of Fedhealth since February 2017. I was happy with their service until I had to cancel the membership. Our company has taken up a new medical scheme for the group and everyone must move to it, which I agreed to. I sent a cancellation letter on the 6th Dec and only today did I receive a response from them saying they require a full month and will not terminate. In between the 6th Dec and today I have sent several mails to follow up and even called their call centre, where I was told that the lady dealing with cancellations is on leave and no one else can handle my matter as there is a backlog.

I am now expected to pay for the month of Dec even though I have cancelled (6 Dec) and started paying the day I joined, in advance. I am also expected to pay up the used up savings (R2500) which means that I now have to pay for two medical aids for the month of Dec.

Fedhealth has taken their time to get back to me on my cancellation and have blamed the lack of feedback on their resources..this is NOT my problem. I want my medical aid membership cancelled immediately and effectively as per my cancellation letter. If I had to pay upfront when I joined the medical aid why is it that all of a sudden I have been paying in arrears?

I need urgent answers!!