I am glad to hear you like the service. Typically, there are prorated charges and credits if a price plan change is completed in the middle of a billing cycle. Additionally, depending on the plan the roaming charges could vary.
You should be able to view a detailed breakdown of all the charges on the invoice as well as MyRogers (via the browser and the app). We would need a little bit more info to specify what may have caused an increase in the bill.
Please let us know if you have additional questions.