Shocking fees masked as admin fees

My Dad was admitted to hospital early September. I recieved a call mid September from mwdaol advising the doctor was not covered in full. My parents are sassa pensioners so I made arrangements for two payments it was not a pot outstanding. I made the first payment and then 2 days after sending proof of payment I get a wattsapp from medaol reading me again about the arrangement and that a R100 admin fee will be charged if I do miss a payment. I was needless to say shocked that a company may charge 15% of the actual bill as an admin fee. I will be logging this with the ombudsman and complaining to the doctor concerned as I find this shocking that vulnerable elderly people who would not question this is being done in. Also a note this is not disclosed when you make the arrangement.