Most credit card companies have implemented programs to detect fraud/illegal use of cards. Most of these programs depend on pattern detection - any usual activity (different than your usual pattern of use) may trigger these types of calls.
Thes programs are designed to detect fraud, and you should welcome this type of computer generated alerts.
I have had several of these types of calls. On one occassion, the credit card company called when I used the credit card in 3 different states to buy gas in the same day. At this time, I had not been using that particular card on a regular basis to buy gas, and was driving to Florida. The sudden change in usage pattern, along with the multiple uses in multiple states raised suspicion that the card may have been stolen (even cloned and used by multiple people).
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