authorized user on a credit card

My husband has been dead for three years. Since then, I have been using a credit card with my name on it and paying it in full every month. I recently tried to redeem some points, which I asked to be issued in my name and they informed me that I was only an authorized user. I informed them that my husband passed. Later that week I charged on that card again and it was declined. When calling they told me that they closed the account. My question is, am I responsible for the $1200 balance on this account that they closed without even informing me and what will the repercussions be to my credit, or any other, if I do not pay. Again, they told me I was an "authorized user." Also of note is that I live in New York state. My current credit score is 814.