Renault refusing to fix my car

I'm not happy with the service that I get from Renault midrand( newroad). My car was towed on Monday because it has problem when I brake it slides to one side, on Monday when they call they said maybe is alignment I need to pay for that, no problem but they will revert to me, Tuesday the other guy i think he said his name is mandla. He said I need to change brake pads because that's the problem I told him I changed brake pads on 10th May but with another company because I believe I have every right to change where I want cause brake pads its not part of the warranty, I explained to him the car started b4 I changed brake pads and it started doing that on February after the car was at the branch since last year September until January, so February I took it lightly because I hardly drive my car. I work from home everyday, so last week Thursday I drove a long distance I almost died with my kids. I'm not even enjoying my car because it seems like it always giving me problems, then on Wednesday I think his the manager he called me and said the reason why the car is doing that is Because I changed brake pads with another company I need to return it there, I then explained to him that no it started before I even changed them, so they say they can't fix it with other brand brake pads, I said I have my old brake pads let's return them because it's your brand that came with the car and I will also provide evidence where I changed brake pads its not on the street its a registered company, with qualified people like them. So I feel like now they didn't check my car they just kept it and using what I told them against me, yesterday I called them to do follow up. No car was fixed since on Wednesday around 1 that they will send a person to come and fetch old brake pads. Today it's Friday my car is being kept, and I need to go home today, they are forcing me to pay R2000 for their brake pads, I refused, the other guy called mandla he said if I don't pay it I will pay R1200 for touching the car, I'm not gonna pay any cent according to my knowledge the car is still under warranty if is broken it need to be fixed for free. Now im stucked without my car and I need to go home I can't go with it while it slides like that, every month I'm paying for the car that I'm not enjoying, the car that is always at the branch, I'm not happy at all and I need my car fixed asap, I wanna go home.