Hyundai Strydom Park - Bad service

My H1 bus in under warranty and also has Road side assistance. My vehicle would not start and we call roadside assistance and they sent a tow truck to take the Bus to Hyundai Strydom Park in Randburg. The battery was faulty and it was replaced but I was told I had to pay for the towing ( R 980 ). When I went to collect it from Hyundai Strydom Park I asked to see the towing company's invoice - they refused to give me a copy or even have sight of it. They said it was their document and were prepared to let me see their ( Hyundai Strydom Park invoice ) but not the one from the Towing company. They said that I can't have my vehicle until I paid THEIR invoice. I said I would if they let me see the invoice they got from the Towing company - they again refused. I contacted Hyundai Head Office Customer Care who also said that I can see the Hyundai Strydom Park invoice and NOT THE ONE FROM THE TOWING COMPANY. My argument is " If I am paying for the towing of the Bus - surely I am entitled to see the Towing company Invoice. It seems that they want to hide the towing company's cost from me