It sounds to me more like a network connection / routing problem than a bandwidth problem.
I obviously know nothing about your setup, but if your system is set up to use one network card and one service provider and you then change both network card and service provider, there may well be some settings in some applications that need to be changed to reflect the change in the network layer.
I don't use Messenger, so I can't tell you what can or should be changed.
SD