overcharged

My friends and I booked for a four day holiday stay at Blue Waters Hotel for four rooms and we were charged for five rooms. We queried this as we thought it to be an oversight but couldn't be help by the Receptionists. After going throw the bookings and calculations they realize the mistake but were told that we will not be refunded ad per Hotel rules. According to them we only have two choices which is to take a voucher for our next visit or use the extra money at the Hotel of which we didn't agree to it. We were then assisted by the Manager but had to be charged 10% for cancellation fee for a mistake that they did. This is surely poor customer service and I wouldn't recommend this place to anyone from now onwards. This place used to be my recommended accommodation when visiting Durban but it is not anymore.