Difficult to help you unless you tell at the very least what kind of router you use, but... usually a router has more than one single RJ45 net connection (the net cable socket), and MY router allows to open ports based on the PC connected to a given cable socket.

For an example, if I open port 8080 on the socket 1, which goes towards my game PC, the other three PCs connected to the other sockets would not be able to access said port unless I enter inside the router's software and enable it to the sockets their PCs are connected as well, and so I believe behave all the other multi-socket routers out there.

Are you sure, in short, that the ports you opened were opened towards the socket where your PC is physically connected to the router?

Your router, to be able to call itself such, should have the ability to assign open ports to each and every computer connected, even the wireless clients, and you might, just might have instructed your router to open the ports you need to wards perhaps an unused socket. Try searching on the manuals.