Medical aid mess up

Hi I am having issues with my medical aid now, in March one of the members on my medical aid was cancelled, but the person went an claimed for medication in April and the scheme paid for it out of my savings. They should not have approved it as the member was already terminated when the claim went through. I have been battling with them since April and now they tell me that I am liable to pay the pharmacy should the claim be reversed. I keep telling them that they messed up, the member was already terminated before the claim went through, I even sent them a membership certificate with the date. Its almost 7 months and I am still waiting for my refund, its over R600.00 The fact remains, they put through a claim in April, for a member that was already terminated in March and now they tell me that i am liable.?? I will not accept this.