If you take your car to a mechanic and they don't fix the problem, there are a few things you can do.
First, make sure that you communicate with the mechanic and explain what the problem is. Sometimes, a misunderstanding can lead to the mechanic not fixing the right thing.
Next, get a second opinion from another mechanic. This will help ensure that the first mechanic didn't miss anything and that there isn't another issue with your car.
Finally, if you're still not happy with the situation, you can take legal action. This is usually a last resort, but it's an option if you feel like you've been wronged.