Hello Hinghie,
Welcome to the community!
Are you located near or around the US border? If not, then it's likely the roaming to which you refer is on extended coverage. There are many factors which can affect cellular reception, including proximity to the cellular towers. You can get an idea of your surrounding cellular towers here. Even though you might be technically within Fido/Rogers coverage, there can small pockets where some devices cannot receive signal from the Fido/Rogers cellular towers. If those areas are also covered by other Canadian cellular towers, your phone will connect to those cellular towers as Fido-EXT.
There is no additional charge for usage on extended coverage. However, you should note that its usage is only meant on a temporary basis. The majority of your usage needs to be on the Fido/Rogers networks. Could your phone have been using extended coverage?
On the other hand, if you are located close to a US border, it's possible that your phone has connected to a US cellular towers because sometimes those signals are stronger. If that's the case, you should contact customer service to inform them of the location where this occurs. There are supposed to be measures in place to prevent the roaming close to the border. However, there may be some cellular towers which have not yet been identified as problematic. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they'll also be able to access your account.
Hope this helps 😀
Cheers
