Trolling? No way this is real! You got a spam answer and you gave them your info!? Not going to lie - that's pretty dumb, man!
Activating new cards is as simple as calling the number and going through some prompts - no sensitive info is shared.
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Conversely, I got a very official-looking letter from Amex saying they had some security concerns and that future charges may be denied if I don't call them. I called the number, but they started off by asking a bunch of sensitive questions without providing answers to any of my questions, such as why I might be calling and the date of any purchase that might have been flagged, so I could try to correlate it to something legit on my end (good in a way, since I could have been anyone; bad, because I wasn't going to answer questions for some stranger.)
Anyway, I chatted online, after signing in to my account, to verify the number was the number for their fraud line. You've really got to do your due diligence and if the prompt you hear doesn't sound right when you connect, then you need to hang up and check again.