Ts and Cs not explained in detail

I rented a car at OR Tambo on the 18th June and I was assisted by Portia. She explained that the total cost for the rental was R990 however the will be a total amount of R4 302.00 that will be held. A refund of R3 310.00 will be done once the vehicle was collected. I remember asking Portia if there will be any additional costs as I will be travelling outside JHB. She assured me that they will not be additional cost