But you didn't share much detail.

Many don't check if MAC filters are turned on. Either add this new device or disable that in the router.

Many use WEP and there are issues there. Set the router to WPA/WPA2 and try again.

And your post has an ODD statement in it that makes me think these routers are not under your control. For a test, go to a location with free wifi before you start making changes and make this worse.
Bob