Discovery says that they will pay and then does not pay!

My husband went in for a back op. Before the op I called Discovery and specifically asked if a back brace would be covered and they informed me that they will cover the back brace from the medical aid. I got a authorization number. Discovery then declined the account and said that it must come from my savings. I queried this and specifically told their advisor, Mulalo that Dscovery told me that this will be covered. Now Discovery is not getting back to me. This is not acceptable. The reference that I have is ********** 913.