Cannot Activate Modem

Upgraded to 1 gig and could not activate modem. Called support and they informed me that I had an incompatible modem with 1gig and that my account was incorrectly flagged to need a tech visit. They downgraded me to 600mb plan and activated modem with advice to get a compatible modem and reupgrade my plan.

I now have a compatible modem and the same issue that it cannot be activated. This time the support people I reached can only read from a script and won’t activate my modem or understand what the other tech support told me had happened. How can I resolve this. I currently have no internet and have spent hours with tech support.