Courier Guy charging more than quoted.

On 26 September I booked a collection via my online profile and the quote [***3] I accepted was valued at R205.85. To my surprise, when I booked more collections the following week, my pre-paid funds were depleted. Looking at the invoices I received, I noticed that invoice ***8 was valued at R1058 and not as quoted!!! I emailed the accounts department regarding my query and I do not get answers, it is now nearly 2 weeks. I can not use my pre-paid account, because according to Courier Guy I owe them money, but according to my quote amount, I still have plenty funds left. I keep on getting the run-around and gets told that they are waiting for feedback from JHB and it is ONLY the MD of the company who can issue a refund [put the R800 odd back into my pre-paid account] This is really poor service and poor communication. But while I know wait for them to give me feedback, I can't continue with my business and have to make alternative plans to ship my parcels, it is costing me money and time!