If the operation was successful his hearing will be static at least until middle age. A hearing test is pretty standard and op says he meets the standards.
So stop being pessimistic. No point paying for another. Go and do the medical expecting the same results and a pass. If it is a just fail hand over the hospital result and ask to retake it.
If it is still a fail then there will be an ENT referral but I doubt this will be the case