End of my wits. Xfinity has no idea why I’m not getting emails from certain places.

For at least the last year, I haven’t been receiving important emails from major companies and organizations including my pharmacy, my utility companies, etc. I have no blocked emails, an empty spam folder. Because of multi factor authentication, I can no longer access my own electric company account to even change email addresses with them. And when I ask Xfinity, they say my inbox is too full and some emails will get through while others won’t, so fine, I deleted thousands of emails and I’m no longer anywhere near full, but I’m still not getting my emails. My pharmacy has started telling people not to use Comcast email address because they aren’t getting through to any of their customers. What is going on?