Overcharged!

My dad booked a wrong date by mistake on Kulula.com and wrote 18May instead of 18 April, the consultant said he can’t cancel and no refund would be given, should he not be charged a certain amount for canceling then ne refunded ? Or is a minimal fee not meant to be charged for date change and then the difference and not be made to pay an amount like you’re re booking?! Not happy about this ! Booking reference is FCNYQE