Internet speeds slow after March 7th "upgrade"

I was notified there was going to be an internet outage in our area for an "upgrade" on March 7th.

Prior to then, I was consistently getting 200-300Mbs on my Netgear CM700 and 250Mbps plan.

After the "upgrade" my speeds slowed to 160-170Mbs and never higher.

Xfinity sent me an email saying I can now get 1Gps service if I upgraded my modem.

I upgraded my plan to 1Gbs, bought and installed a Motorola MB6611 2.5Gbs modem.

I am still getting the exact same (160-170Mbs) speeds...

After many calls, they finally sent a tech out. He tested the line and said it was fine and can't do anything else since it was my modem.

I switched back to the original modem - still the same thing.

Something clearly changed after the supposed "upgrade", but since I own the modem, they refuse to do anything else to find the issue.

I am only getting about 1/6th of the speed I am paying for. 

What else can I do to solve this issue? I have been dealing with bots for 4 days straight and it's very difficult to reach a real person.