So im trying to port forward some ports for my nintendo switch but they are always closed and arent getting port forwarded. I have two routers my main router that gets the internet (Zyxel VMG8623-T50B) and a second router that is connected from the wan to the router (Tenda AC10u). I have tried port forwarding both but to no avail , i also tried dmz but still nothing. Is there a way to fix it or i must call my ISP.