Wifi Not Connecting With The Yellow Wire?

So, I have TalkTalk broadband. For the past few years I have used the WiFi not connecting with the Yellow wire. But now I want to move a PC up stairs. I brought a longer White wire so it would reach from downstairs where it is plugged in to upstairs (if I just plug in modem in upstairs it will not connect) So this is the idea I have downstairs the phone that is plugged into another white wire extender that leads from the main plug in the wall. In that extender is the phone and the OTHER extender that leads upstairs to a room just above. The extender leading upstairs has the internet modem plugged into it. now the extender white wire from the other extender downstairs has one of those white square plugs. (the ones that go from the main socket and the phone and modem connects too) And that Square plug is where the modem is plugged into. BUT now this is the annoying part! it will not connect to the internet without being in the same plug as the phone downstairs!