Only make this change if the reboots don't work...
Network > Interfaces > Devices (tab) > wan > configure (button) > MAC address
If you plug a different router or a computer into the cable modem and it successfully gets an IP, you will then look for that device's MAC and enter that in the field for your wan.
But as I type this, it looks like you're in businesss! (leaving the above for reference for you later or for any future readers).
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Thanks! 