Well there are a few things to check here.
1- The basics, is data activated on your phone?
2- Is there a restriction placed in the account by accident (possible)
3- Is the phone using the correct apn in the settings? (settings -> more -> mobile networks -> Acces Point Name )
----- The APN should be "media.ng" with some other details in it
I would also try giving technical support a call when you have a chance if you don't see the issue yourself. (try calling from an other phone that way the G4 will be free)
Thanks Kira. Your latter solution was the key - call tech support. It turns out that I had the wrong type of SIM card (wasn't even aware that was possible) and the tech was able to diagnose that and referred me to a Videotron outlet. Got the proper SIM card, and data works now. Yay!