Discovery handing me over while I have an existing membership with them.

I was on Malco medical aid which is under Discovery. I changed jobs and they changed from Malco to Discovery. They gave me a new membership number without a waiting period. The pharmacy processed the last medication on the old membership number. Now they handed me over saying I'm owing Malco. Yet they can see that I'm still with Discovery. The last person I spoke to from Discovery, promised to sort this out by transferring the invoice to my new membership number. Now I get annoying messages, and calls from the company they handed my name to.