Medical aid - But yet nothing is really covered when you need it

I fully understand that you covered for what you pay for.I understand that things like x-rays or scans is not covered on my plan.Its something that wont break the bank.But what i dont understand if you have a cancer scare and need a biopsy to be done at the hospital this is not covered and then you get slapped with a R7000 bill.Yes ofcourse everyone has that type of money just lying around. Then looking at maybe changing plans then the next level plan is double what i am paying today. i just think medical aids should do better.