You have fixed wireless service (antenna on the roof)? In case they are tracking the MAC Address of the device connected to their system clone your computer's ethernet MAC Address to the router's WAN. There will be an option to do this in the router's config pages, maybe in the WAN section or maybe in an Advanced or System section.
When switching from computer to router you may also have to power cycle the PoE adapter and/or whatever other device (which I would loosely call a "modem") is between the antenna and the PoE to "convert" between wireless and ethernet.
When switching from computer to router you may also have to power cycle the PoE adapter and/or whatever other device (which I would loosely call a "modem") is between the antenna and the PoE to "convert" between wireless and ethernet.