VW Bloemfontein is misrepresenting

I took my cat in several time in to vw because the engine light was coming on and they struggled to fix the problem eventually in September the problem was sorted out and on the 29th on November I took the car in for major service and nothing was wrong with the car except it had to be serviced when I collected the car the service provider reiterated that I know that the car has an engine problem and I had to sell the car and I acknowledged that but when I left the dealership the car was loosing power which is something it was not doing when I sent the car so I went to a filling station to check if there was oil in the car which is something that vw Bloemfontein never replaces after a service and there was no oil in the car but after I filled the oil in the car the power of the car was still doing the same my problem is the service pro idea made me sign and acknowledge that I knew the car was having power problems which not the trading why I took my car in and it was not having the problem it has after service I feel the service provider is taking advantage of a situation and the problem is that I am paying for VW to brake my car every time