Diagnostics payment

I took a 2003 model Renault for diagnostics and was told I would have to pay R900 just for that.I was happy for Renault to go ahead and fix the car but they then wanted me to wait 3 working days before I could get the car back again.Because of this long waiting period I did not want them to carry out repairs but yet I still have to pay this diagnostic fee eventhough I was happy for them to fix it but poor service meant I needed to take it else where as I need the car.It took 24hours for them to get back to me with the diagnostics which I think is unacceptable.