While I do not like Companies threatening me, I also make sure I know what I am paying for before I pay it. I am little confused on how they were able to get your card number. You said they would not take it from you, nor would they take it from your son and daughter in-law, but somehow the provider got it. I would never give anyone my CC Number unless I knew what I was paying for, and due to the rampant fraud these days, I would not take one from anyone who did not have ID and the physical card, I know here they will not do it unless you are a company.
I have used a mobile mechanic, they do have a minimum on-site charge, which was explained to me when they arrived, as well as the hourly rate and any parts cost when he needed them. Unfortunately you are at the mercy of the actual service provider when you go that route. Always ask for an estimate upfront before they do any work.
