I suspect that you do have a call reboot rule configured in your router. You can delete this rule by navigating the router WebUI > Services > SMS Utilities > Call Utilities tab. There you should see all your call rules and a Delete button near them.
Regarding the removal of constantly connecting devices to the WiFi, I would like to suggest for you change the WiFi password. That can be done in Network > Wireless. Please press the Edit button near your access point and press Wireless Security in the newly opened window and change KEY phrase.