Unfortunately, Xfinity service is not available at this address. I live in a major city and I get this reply when I'm trying to get service

I had service with Xfinity for 10 years, I move to a different apartment, still in Chicago, and I couldn't get service at my new apartment. When I enter the address on the Xfinity website, I get, "Unfortunately, Xfinity service is not available at this address" and it instructs me to a website called "SmartMove" to figure out who my provider is. When I enter my address on SmartMove, it takes me back to Xfinity since that should be my provider, its an infinite loop. I tried talking to Xfinity customer service on the phone and chat and even went to a Xfinity Store to move my service with no luck. All the Xfinity customer service employees tell me is that the address is not serviceable, even the employees in person that know my address is in Comcast territory, have no reason to why they can't provide me service. So I gave up and went with AT&T internet and U-verse for a few years and I am feed up with it. AT&T is horrible, slow speed, router resets everyday, picture quality not great, delays in shows; which is irritating when watching sports (getting text from friends about homeruns or touchdowns I haven't seen yet) and the cost is getting ridiculous, especially for bad service . So I am trying to get Xfinity back. I live in the heart of Chicago, with apartment buildings on both sides who can get Xfinity (I've entered their addresses on Xfinity's site and didn't get a "service is not available" message.) No other tenant in the building has ever had Xfinity, I know some have tried and also failed. My landlord says she has never signed any exclusivity deal with AT&T for the building and does not oppose having Xfinity in the building, she only opposes satellite dishes. The apartment building is well under the 300 feet from the Xfinity physical network, which I read about as a requirement for service, and its only a two level building, not a tall building. I also have Xfinity Mobile, which I cannot make changes to, like upgrading phones, since I don't have Xfinity internet and I do not want to change mobile companies. I just want Xfinity internet and cable back and I am tired of just being told it's not available without getting a real reason why and without anyone just sending a technician out to try. I'm sorry for the long post, I just want help with this issue.