You can only change your plan once per billing cycle. Unfortunately there's nothing you can do except call in and see if they're willing to throw you a bone. But just warning you, I don't think they will.
Hmmm Okay thanks then ! I've been on wait on the phone to get some help for 47minutes now actually ... hopefully they'll pick-up eventually, I need the Data today and I'm not keen to pay 5CAD per 100MB ... Thanks for the answer though