Looks like Fido's latest cash grab is to randomly charge people for roaming even though the settings on the phone like "Data Roaming" and "Mobile Data" are set to "Off". All customer service does is to say the charges are legitimate without anything to back their claim up. My wife also had the same problem so now we are both currently looking at a new provider.
I'm sorry to hear you were charged for roaming if you did everything you could to avoid charges.
We strongly recommend making sure your phone's airplane mode is activated to make sure you don't get charged for Fido Roam. Even if your data roaming is disabled, your phone can still connect to a foreign network and receive calls, texts, which would in that case trigger the Fido Roam feature.
If there is truly no usage, there is always something we can do.
Hope this helps.