Account no longer active AND Can't activate personal modem

Context: I was going to move to an apartment 2 months ago, so I started the process to move my service from my old apartment to the new apartment. Then, due to an emergency, I didn't end up moving into that new apartment, and remained at my old one. During that month (June&July), I cancelled the transfer of service to the new apartment, and retained internet service at my original apartment.

I then moved into a completely different apartment at the beginning of this month, August, and started the process to transfer my service again. I plugged in my router and modem at my new apartment, and to my surprise, I still had internet access. The phone app still showed that I needed to activate my modem, but I was already connected to the internet. I still tried to activate my modem in the app, but it returned with an error saying "Sorry, we're having some trouble".

I've tried completely resetting my router and modem, but the issue remains; I have internet access, but Xfinity thinks I still need to activate the modem.

I assumed all was fine, since the app showed I owed $0 in the billing section. Up until today, when I received a text from Xfinity's 266278 phone number, telling me that there was a past due balance on my account. Again, the app, and the website, both show that I owe $0.

I assumed the issue was because my modem still wasn't "activated" in Xfinity's system, even though they were still providing me with internet access at my newly current apartment. I attempted calling the self-activation phone number, and it thinks that my account is inactive AND that I live at the apartment that I didn't end up moving to in June.

When I go on the website to try to change or edit my internet plan, it says I'm not the account owner.

So, I need help getting full control of my account, I need help activating my modem, and I need to make sure I'm not being charged for service at an address I don't live at.