Authorisation for life changing procedure rejected

my son needs a rhizotomy done due to a back injury, my neurosurgeon a well known an highly educated doctor requested the prosedure to be done, but a telesales consultant at discovery rejected the pre authorisation stating he needs to have facet joint injections done which discovery does not pay for, i pay my premium every month without fail yet they reject a life changing procedure for a 17 year old child whom have been confined to lying down as walking and standing is extremely painfull. he has been diagnosed with Lumbar Spondylosis at levels L3/L4 L4/L5 L5/S1 and i had those facet joint injections in january and after 2 months i was admitted back to hospital i also dont havd 10k fir these injections. why would a surgeon want to do this procedure if he did not think its necessary. so instead my 17 year old must live with cronic pain, jelly legs and a numb right arm