Capitol One sueing me for $800, really?

So a controlling ex of mine would not let me pay my bill and kept using my card and now I am being sued by Capitol One for the $800 bill. I would have paid it if I had access to my own funds, ya know? And no one lecture about leaving an abusive realtionship either, I had no where to go. But now that I am being sued I am PISSED and want revenge. Can I sue my ex or can I fight Capitol One since it is only $800 they are sueing me for?? I am clueless about all this. Thank you!!