Did they connect a LAN port of the new modem to the WAN/Internet port of your existing wireless router?
If so and if your wireless router is not running in AP mode then it's doubling-NAT'ing and your wireless router is possibly now on a subnet imposed by the new modem, different from what you had before.
How is the Spectrum modem connected to your wireless router? IOW, what is the label on the ports that are connected from the Spectrum modem and to your wireless router?
I will have to look at Port names when I get back home. The modem only has one and it goes over to there wifi box to control Xumo TV box. That has ports on it and one of those ports go over to my router. I tried plugging my ethernet cable from my NVR into that still no go.
I know my router is working as it controls other stuff in the house.