I signed up 940 Mbps and typically the speed test shows less than 100Mbps. Is this a scam?

Could you provide the makes and models of your modem and router?  I'm thinking you may have an older port...Fast Ethernet (100 Mbps)...somewhere in your network.  Maybe not.

For all troubleshooting, let's bypass the router and always connect directly to the WAN port of your modem.

Cox does not guarantee speeds. I had to file a FCC complaint and that is when they clued me in on that. So they feel they can charge you as if you were receiving 940mbps while you still never reach those speeds.