Welcome to the community!
I think Fido is attempting to limit fraudulent activity on accounts. Fraudulent behaviour can include multiple access attempts or changes to a particular line or account. While it's true that making multiple changes to an account can be for legitimate reasons, they cannot overlook the possibility that nefarious actors may have access to a customer's information.
However, you should note that this forum is community-driven and not intended as a venue for customer services. As such, we would not be able to look into your situation. If you would like to discuss the issue, you would need to contact customer service. 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 😀