I need help with a duplicate account issue

I have a duplicate account issue that has caused me to spend MANY hours chatting with agents.  Even though the last agent said the inactive account had not been removed, it has not, and I'm still having issues.  When I log in to my account, I'm not offered a choice between the two accounts, but it won't let me change a payment method because it says my account is invalid.  I've been an xfinity customer since it was Comcast and only had cable TV, and I've never had such a problem.  Does xfinity have an ombudsman or some other way to fix this?