Goodness, you are so mad at yourself! I think you are maybe too shy to speak up or you are like me and just don't want to "make waves". I just hate fussing about things but I also hate being taken advantage of so I am working on getting a bit bolder. I doubt that the guy charged you twice because he knows it would show up and he would lose his job. Give yourself a break there's nothing wrong with being quiet. You know you have the problem so just take steps to try to get better about it. It takes some work but it can happen.