Unhappy client billed additional amounts

I rented a car for my trip to Durban via the internet and the rental was done via rentalcars, however I called them after receiving the quote because of the different rates for the 1st 5 Days and a other rate for the last 5 days but was told that the amount could change on the day I collect the vehicle, so on collection of the vehicle I paid the amount indicated on my Agreement which I had to sign as acceptance and the consultant confirmed that it is the full amount paid for the 10 day rental period. It was raining when I picked up the vehicle and it being late at night I took the car, however the car had such a terrible stench for the full 10 days i was using it, I returned the car on the correct date and had confirmation from the returns division that all is in order and even went into the office to confirm if all is fine and that there is no further payment required from me. On the Monday following this I see that Thrifty had indeed debited my credit card with a further R610.00, so I called them only to be given the run around, first the lady who did the debit was not available and would call me back, she did call me back but could not tell me exactly why this amount was taken from my credit card, she called back later the evening and told me it was a short payment as the amount I paid and signed for on the Agreement was not the same as the amount on the quote.

I do believe that this is not my mistake and I cannot be held responsible for their incompetencies and their system errors as this was the excuse given to me by the manager Rennie Perumal, because they have access to your credit card, they have the right to debit you with any amount they find to be shortpaid (without notification to you), i think this is real Bull........ I don't know what else to expect from them and if I can help I will not advise anyone to use Thrifty as they are not clear and transparent in their dealings.