Still waiting for my claim to be paid

I took my wife to a Doctor's Apointment of which we had to Pay R900 Cash. We then Claimed it back from. Discovery. They then Requested a Invoice from the Doctor's and after all the Trouble we went through to claim back the money they said they are Going to pay out only R500. The Next day My Wife received a message saying that they paid the money to the Doctor's. So No the the Doctor's already received more than they carged. My wife sent an email to the Doctor's requesting the money back untill now we still didn't receive any payment. My wife sent an email to Discovery as well which received now awnser untill thus far. I personally feel it's Discoverys responsibility to get my money back from the Doctor's as it is them who payd the Doctor's twice now