Discovery medical aid refusing to issue medication

Discovery medical aid put a block on my son's medication despite having a script from a specialist paediatrician. The reason for the block according to the agent i spoke to at discovery is that the medication is being abused! Since when do discovery medical aid have the right to refuse to dispense medication prescribed by a paediatrician. Now i have to go back to the pharmacy for the 3rd time discovery is wasting my time petrol and airtime.