I can't do anything with my account won't let me stay signed in

I set up an account, selected my internet plan, put my checking account information in, and now I can't do anything because everytime I try to do something it prompts me to sign in, only to immediately sign me out. I've tried on my phone and laptop. I can't use the app because it tells me I need to be an xfinity customer. I'm at a loss for what to do, and when I try to just set up my modem it tells me that I need to use the app