after obtaining pre auth, it has been revoked

I have chronic sleep apnia, and have been told by doctors to get a CPAP machine.<br> After contacting the medical aid via phone, and 3 days fighting, they finally said they finally gave me a pre-auth and said they will pay it out the chronic section for machines, Max of R5040, even though the machine costs about R10k. (I had to supply the doc letter and basic costings of the machine)<br> Now after I purchased the machine, from a cheaper supplier, they are refusing to refund me the pre auth portion of the amount.<br> I have all the reference numbers of all the calls made.<br> And now response from them takes forever, and they are not being helpful, just replying with useless emails stating they won't pay, and not giving any useful feedback.