Citibank Reward Credit Card Closed my Credit card For Absolutely No reason.

My husband went on a business trip and he took his clients out for dinner and his credit card was turned down at the Restaurant and Citibank Mortified my Husband. When he came home and went online and Citibank (never notified him of any reason why they closed his credit card down)? but they made my husband look like a complete fool; This Citibank is irresponsible and non-professional. You do not just close a customer's credit card when they make their payments above and beyond the automatic payments that my Husband set up with Citibank and he pays above and beyond the minimum payment every month and Citibank Thanks you by Embarrassing a long time Customer by closing their Credit Card and you embarrassed him... When you do this to your customers that tells you what type of a Bank you are?  A very unprofessional Bank. Warning to all people who are thinking of opening a Credit Card with Citibank. I would not.