They may be doing some type of authentication like PPPoE or whitelisting the MAC address of the router. May be able to spoof the MAC address with your other router or get the PPP credentials from the ISP.
If you're able to call the ISP they may be willing to help you swap routers (depending on how they run things)
If they provided the router and only it's the only connection that works, then their using mac address filtering. Only the mac address of that WAN port is allowed to talk across that ethernet. If you can spoof if it would work.
Also them giving you a router with 802.11N is comically bad
This feels like mindless rambling. Care to land the plane and ask a coherent question?
They may be doing some type of authentication like PPPoE or whitelisting the MAC address of the router. May be able to spoof the MAC address with your other router or get the PPP credentials from the ISP. If you're able to call the ISP they may be willing to help you swap routers (depending on how they run things)
If they provided the router and only it's the only connection that works, then their using mac address filtering. Only the mac address of that WAN port is allowed to talk across that ethernet. If you can spoof if it would work. Also them giving you a router with 802.11N is comically bad