Cancellation Dispute

I enrolled my son in Intec Late January, and cancelled the contract 21st February 2015,a few days out of their cooling off period.All books were returned.I received feedback in June that I am liable for 80% of the total cost of the course,as it was out of cancellation period.Their contract states a reasonable cancellation fee.80 percent is unreasonable.I have dealt with many fools there,and to date this is not resolved.They have even kept my deposit of almost R3500.So in essence,I have received absolutedly nothing from them,and am still awaiting feedback.They have since blacklisted me.I call the college every other day,but no one knows anything,or they say they will get back to you but they don't.,