My seat belts will retract but wont catch if I yank on it, even with the break on. This kind of renders the seat belts themselves useless.
What causes this and how much should it cost to get fixed?
Your seat belts have momentum based locks. They aren’t connected to the brakes in any way. While you’re driving, if the car rapidly slows (for any reason, braking included) or makes a sharp left or right turn, the seat belts will lock. This is the way that it is supposed to work. You can’t test it with the car sitting still or by lightly braking.
Yanking doesn’t do anything. Go to an empty parking lot and slam on the brakes. They should catch then.