Wouldn't surprise me if the "suspicious charge" your card is suspended/cancelled over is that $200 bill to the ATF.
I lose more faith in the banks' credit card "monitoring" services every day.
The last time I had "suspicious activity" on my card, they just cancelled it and reissued a card, without even giving me the opportunity to confirm or refute their suspicions. When I asked what suspicious activity there was, I was basically told it didn't matter because they had already cancelled the card and it was a waste of their time to review it.
EDIT: I'm pretty sure I've mentioned it in here before, but every time my card has been suspended or cancelled, there have been firearms related charges in the list of "suspicious" ones that they have asked me to verify. Every. Single. Time.