Incomplete service on my car and part lost

I would like to state that I had taken my car in for Service at the Bosch(Finla) Service center that's situated at the corner of Schubart Street in Pretoria CBD and I was given the most Horrible service of all, Firstly I took My car in for Diagnostics, then they sent me an invoice then later send me a different invoice stating that there was an error with the previous Invoice.Then when i finally agree that They can go on an perform the necessary repairs on the vehicle, when going to collect the car I then get told that there's a different amount for when you paying cash and there's a different amount for when you paying by card, I then made the necessary financial adjustments and then paid them, but then after I took the car because I was in a bit of a hurry to get to work, i noticed that the shocks were still uncomfortable, just like before i had taken it to them,they had lost my lock nut and one of the sock mountings had lost a cover.I had asked the guy who booked the car in to check what was the problem because there was a strong petrol smell, but still when the car returned the petrol smell was still there and He didn't tell me what happened.I then noticed as well that My steering was a bit stiff and when I checked the transmission oil, it was brown in color, my sock and dismay when i notice, I then approached them on the missing shock mount over and they gave me another one which was not identical to the one they had lost, i then told them about the missing lock nut, they stated they would buy me a new on, to-date I still haven't received it.They stated they had replaced the shocks but those shocks still feel as worn out as when I sent the car in, my car still had the clunking noise that it had on the suspension just like when i sent it in and they stated that the problem was resolved.Personally I feel the person to whom they had assigned to my car was one, a delinquent , and two didn't have the slightest idea what they we doing.When I did a follow up about my issues I was told that Jay is on leave, So I couldn't get assistance because he was on leave, and When i asked one of the mechanics to take a look at the car, the fat bloke mechanic told He's busy and couldn't attend to my car,so tell me Bosch is this How your treat your customers, your charge t hem high amounts of money then give them no service, i find this very alarming