Xfinity Support

Back in June I was given a promotional upgrade to the gigabyte service and this came with receiving a new modem from Xfinity.. This is a rental property of mine so I am not there everyday. As soon as I installed the modem i was experiencing intermittent connections issues. Assuming I had a bad modem I went to the Xfinity store and had it replaced. After replacing the modem I discovered I had the same issues. Multiple chats with Xfinity but still over 4 months later still have the same issues. Had a senior technician to the house yesterday and he replace the cable from the Xfinity box and ran a new cable back into my house and yet we still have the same issues. Technician also replaced the modem two more times as well with the exact same result.  The technician suggests the issue may be with my account and suggested customer service can help me.. After 4 hours and at least 5 people on the phone last night, the last guy said he needed to escalate this issue and had me hold for over ten minutes and then the call was disconnected. Of course they never called me back so I had to start all over again. Today I tried to connect to xfinity wifi and had the same issue with the connection issues.  Before this upgrade to my service I did not have any issues with connections. Please help me understand what I can do at this point as even the technicians cannot assist anymore.....