For any number of reasons you are not responsible for this charge. You weren't the person who put the car there. You didn't know about it. They have issued the penalty to you as registered keeper of the vehicle. That is incompetent. If there is any liability it is on the driver of the vehicle who put the car there. You comments about the garage being the legal keeper and the "famous case" aren't really in point except to the extent that you can't be held responsible for whoever was driving and parking the vehicle whilst it was in their care. You should ignore these demands assuming you have already explained the situation to the parking company. If they sue you, they will lose on the narrative you have given me. I hope that helps. Please leave a positive rating so that I am credited for my time.