ACSA parking ******* at OR Tambo Int airport

We were charged over R500 for parking at OR Tambo Int for about 3hrs. We unknowingly parked in the long term section of the parkade. The parking attendants claimed there was nothing they could do to override the charge, even though the signage when entering the parkade is totally inadequate. The staff also indicated that this is a common occurrence and many people get caught out and park in long term.