Customer owned modem speeds purposely slow?

I recently purchased a new CM2000 modem, activated it and now I don’t get the speed I am paying for.  I have had issues trying to speak to a real person over the phone and using chat isn’t ideal.  The modem is on the approved list and I have tried all the troubleshooting steps but my speeds have not improved, they have gotten worse.  I don’t like being forced to pay for equipment when there are options and the people over chat think everyone is an idiot.  How do I get in contact with a higher level of support, if that’s even possible.