Europcar refuse to pay my deposit

Good day. I rent a car by europcar tygervalley. I return the car on 5 January. When I return the vechile the inspection was done and there was nothing wrong with the vechile. I want my deposit back and now europcar car tells me there a mark on the bumper. That unacceptable. Cause I did return the car with no damage and clean. They were quick to get my deposit but do have a problem and excuse to refund me.