Will Not Pay For My Crutches - Discovery Health

I am very disappointed in discovery health. One the scheduling of my sons operations (leg break and traction for 9 months) I purchased a decent set of crutches. Smart crutches so that my 11 year old would not have blisters on his hands again like the last leg break. I bought these directly from the supplier and paid cash for them, the amount paid falls well within the limit. They were also a lot cheaper than at any pharmacy. On submission of the claim to the medical aid we were told that because the invoice was not made out to the doctor they will not pay it. Really, do all patients only purchase crutches from the actual orthopaedic surgeon. I have the hospital authorisation for the operation where it was clear they were going to break his leg and put him in traction. I do not regret getting decent crutches for my son but am really disappointed that my MEDICAL AID has shrugged responsibility for the account.