My bank uses a fraud detection system that calls you if suspicious activity is detected on your account. It then asks you to call back a number to verify the account activity. Every time they call, they provide a different callback number. Searching for the callback number online yields only one result, which is the fraud detection systems web page telling you to NOT trust phone calls of any kind (their advice is solid, but it tells you to not respond to their own legitimate calls)!
The only time I ever triggered fraud detection system on my card I got a text message from bank that was "Your card is blocked due to suspicious usage, please call 'number'". And the number was also some random unlisted one.
Only reason I didn't just ignore the thing is I did make a purchase on new website a half an hour before.
Called my local bank and they confirmed this was legit, I almost went off on a full rant about how bad their protocol is for this.
Yeah, I'll pass.