Not getting close to150 download speed - I need help

I am not getting anywhere close to the 150 download speed. The max I have been getting is 40MPS but it averages 25 mps. Upload speeds run from 800K to 2MPS.  I have used Cox speed test and DSL Reports speed test. I am also getting really bad lag in my connection and random disconnects.

I called Tech support about this issue. She cleared the buffer then it took forever to get my internet back. Then I was told I needed a new modem and that it must be faulty. Not that it looks faulty due to X issue. The modem I have is fully capable of meeting the speeds and it is only a year old. It's a Netgear RNC1000 which I own. All this started being a problem when a COX tech worked on a connection box across the street. The tech refused to listen to me. I don't want to pay for a service that I am not even getting.

I need help!