Welcome to the community!
What phone do you have? Where did you purchase the phone? Was it from Fido? If not, have you verified it has the necessary compatible bands/frequencies? You can verify those here.
If it's android-based, have you verified that the phone is using the proper APN setting? If the phone is LTE-capable, it should be using ltemobile.apn. You can verify the proper settings here.
If your phone is an iPhone, have you tried to reset the network settings?
Hope this helps