Incorrect final bill & cannot get it corrected

Hello, hoping someone out there can help me. 

I received a final bill from my canceled service. However, the reason I canceled is because Xfinity never sent me a modem (I called twice to resolve this problem before canceling). Now the final bill says there's a charge for breaking my contract. I need someone to remove this charge, since the service was never officially started. 

I've called multiple times to get this resolved. Because the account is already canceled, the automated system says there's no such account when I enter the account number. I've managed to get through to a real person once or twice, but because I'm in a condo, they say they can't fix my bill themselves and transfer me to bulk accounts. The bulk accounts line puts me in an infinite loop of entering my phone number and account number and telling me neither exists. HOW DO I REACH AN ACTUAL HUMAN TO FIX THIS.