Welcome to the community!
Fido is supposed to have an accidental roaming solution in place for those who live near the US border (see here and here). It's possible that US cellular tower has not yet been identified as problematic. You would need to discuss the matter with customer service so they might identify that location as an issue. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they will also be able to access your account. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀