Pre Authorised and not paid

My mum is a stroke patient and required botox injections which was motivated for & feedback received on the 4/9 authorizing this from hospital plan as her savings is depleted(ref ***).I did contact discovery & advise them of the date of the procedure as requested, 22/09.On the day that we arrived at Dr Staub's rooms we were given a script and told to purchase the injections as he does not purchase the injections as he had an experience with a medical aid that didn't pay.We then contacted discovery and advised them of what happened & asked if they will pay the pharmacy if they give us the injections & were told that they would.The pharmacist then spoke to discovery & they advised him on the details & he will get payed.On the 13/10,I received a call from the pharmacist telling me that discovery had not paid & he did liaise with them & was not successful. We called discovery & sent docs through & was told by both Reshmee & Zakia that the pharmacy WILL receive payment as a block that was on the system needed to be removed. On the 23/10 we received a call to say that it will not be paid.This is not on.How can a preauthorized procedure not be paid. I await a favourable response.