Why can't Cox Fix My Internet

Ever since I moved into this house years ago, I have had intermittent connection issues. Multiple service reps have been out here to "diagnose" my connection, but no one can ever seem to pinpoint the cause of my connection.

I have recently cut everything but internet (because we know Cox is a monopoly in this service), and I continue to have connection issues.

It's only the UPLOAD I have issues with. 

I pay for: 100 Mbps DOWN, 10 Mbps UP. My last test I received: 86.33 Mbps DOWN, 0.00 UP, with a 44% packet loss (29 ms latency, which is acceptable). It has always been an issue with my UPSTREAM connection. Multiple modems being used, no change. When performing this test, I always disconnect from the router and connect straight into the modem so we can ensure the router is not causing the issue. I have used Cox's provided routers with the same issue, but currently I am using a retail router.

I am so tired of paying so much money to get so little back. I would just like to get a working internet connection

Edit:

I would like to mention this issue is sporadic. Sometimes it works, sometimes it doesn't. I can run a test with a normal range then come back in 5 minutes and I get the above. 20 minutes later it may work again if I am lucky, but if it does, then I can expect it to go down within another 10-20 minutes. No consistency, which is what makes diagnosing my issue such a problem.