After doing some basic research as I am not very familiar with the $45 monthly plan, it appears that this plan is a "Walmart exclusive" plan. Apparently in your case, the selection of the $45 plan from the $25 monthly plan was not processed somehow. In order to activate or switch to the $45 plan, you can do so by calling GoPhone support at 611 or 1-800-901-9878 and saying that you would like to switch to the "$45 Walmart 1GB plan."
Hope this helps!
Hope this helps!