Overcharging waybills, no customer service.

For the second time The Courier Guy has managed to turn a 26x16x112 4kg parcel into a 78.5 cm x 46.2 cm x 97.3 cm 71kg parcel quoting a R220 but charging a R3686.90. With no one getting back to me, my account frozen, there is no way we can ship anything to our paying clients, waiting for their products. How do small businesses survive such blows from courier companies? Is the courier guy that big that they don't care how many small businesses they ruin? No one, not even the area manager, could care to come back to me with regards to the refund / credit on our account. Why do the small companies pay the price for the larger companies mistakes?