My guess is that your spending patterns triggered the initial fraud alert ($2k at a grocery store on a brand new card), which after being unlocked was followed by two $1,500 back-to-back purchases. These are not the typical charge patterns for a new cardmember.

You then hit your credit limit before paying off any of the prior balance, which is another red-flag for sure. I'm reasonably certain they would have flagged this behavior as manufactured spending and/of a fraudulent application, which then caused them to look into your account and reconsider their potential exposure.

Personally, I wouldn't bother trying to untangle this mess with BOA unless there is a real reason you need to have their credit card -- rather, I would move on from them and try again after a year (leaving the bank account open).