demand letter reacived

I closed my bluebean credit card last year they cornfimed closed there was money they owed me they credited it in my bank account I was so suprised when I got a demand letter that I still owe that credit card.I called the customer service to understand what's happening I was sent from pillar to posts I'm very upset I sent bluebean an email no body answered me back. this is very bad I need this to be rectified immediately