I opened up the app and saw all the plans available and switched my $29 "10" GB Canada US Mexico to the "20" GB Canada US Mexico and it will start on my anniversary. No problem at all!
I had the $29 10 GB , can,US, mex.... I looked at all the other plans available and it showed the 20 GB $29 so I switched to that one and it will start on my anniversary date. No problem at all!