Work done without approval

My partners car was in an accident. The car was sent here for repairs by King price. It was driven here mind you. 3 weeks later they call and say it doesn’t want to start they need to change the ignition. We said no we delivered it working. They then went and changed it anyway and want to charge us R2500 for that when we accepted no quote and said no. I’d like a manager to call me to explain how they think that’s legal?