I need an easy way to really manage my account

Right now, the only thing I can manage is Xfinity mobile. I have been a triple play xfinity customer for... I don't know a bunch of years. My needs have changed, options have changed, and yet one thing that has not changed is my ability to self-manage what I need and want. Xfinity make it looks like I can modify my account, but I can't. Everything I try to look at new offers, or modifying an existing service, it bring me to the page where I should be able to do that, and then... That's it, I cannot change any of the services. You have clearly build the platform for your users to able to do that. Why can't we use it?