When someone attempted to use my card number to place 3 flower orders to an 800 number (name did not match) the florist immediately reversed the charges, and that prompted the credit card company to also refuse an attempted internet purchase from a Florida travel agency, and advise me of the problem.
The only other unexplained charge was $205 from a Walgreens in Berwin, IL. I asked the credit card company to provide address of the store, date of purchase, and who signed it, because I was on vacation in California when it posted and could not imagine such a purchase from a drug store. The charge quietly went away. The fact that they were already aware of attempted fraud may have helped.
I would certainly suggest that you request from them specifically when and where the charge was made, and a copy of the signature. If you are sure you were not in California then, it sounds like either a glitch in the system or fraud.
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Not an expert, just a potential victim