I really, really know about that kind of overwhelm. I also have difficulties with bills and general executive function when I'm in a period of serious anxiety or depression. It sucks. I'm sorry.

Are you a list-maker? Sometimes in those times I make a list of tasks and try to accomplish the easiest, least unpleasurable ones and that helps a little. I find it easiest to start with stuff that can be done online, then by phone, snail mail and lastly by in-person meeting.