I'm going to suggest that possibly the problem wasn't that they were concerned about the charges on your card. Since you had been using the card without issue and then suddenly right after the New Year, it was locked, PERHAPS there was a change that was activated as of the first of the year and you didn't receive or respond to something that needed to be done on your end. So they locked the account.
Perhaps a simple call to the bank could have told you that they had sent out a new card 5 months prior and were canceling your old card as of 1/1/16. When you continued trying to use your old card, they sent the secured message to call them so they could find out if you never received the new card or lost it or just didn't realize your old one had been deactivated.
Again, just assuming they are making life difficult for you - without even knowing WHY they did what they did is very dramatic...
