Hello LilySi,
Welcome to the community!
Sorry to hear you've received unexpected roaming charges. Although you might already be aware, the Fido Roam charge will incur when you use your device to make or receive a call, send a text message or use data while abroad. While receiving SMS would not incur the roaming charge, it's worth mentioning that the data contained within MMS (incoming or outgoing) would be considered roaming data and charged accordingly. You should note that MMS are not solely restricted to pictures or video messages. Messages with subject headers or group messages etc are also considered MMS.
You might consider disabling any MMS auto-retrieve settings on your phone. You would then receive a SMS notifying of a MMS (no charge) but the data contained would not download automatically. You could then choose whether or not to download the associated data contents. You should also note that, with the exception of Wifi-calling, MMS does not generally get transmitted via Wifi. Downloading MMS while connected to Wifi would likely incur roaming charges. That said, if your device is supported for Wifi-calling, some types of usage would be considered roaming.
I understand you had your roaming setting disabled. However, you should note that some phone manufacturers might not disable all data when that setting is disabled. They consider System data different from User data and allow data they feel is necessary for the phones to function optimally. Unfortunately, iPhones are notorious for that type of behaviour. Disabling iPhone's roaming data setting doesn't disable all types of data usage (see here, here, here, here, etc). I understand some of those links are dated but there are more recent other examples as well. An explanation I have read is that devices connect to Apple servers for certain essential functions so it is allowed despite data and roaming data settings disabled. Those little bits of data (ie 40 kb) are typical of their requisite data transfer. Unfortunately, I don't think there's an official solution as Apple tends to deny it's an issue.
You should also note that customers would not receive a notification for every day of usage. Unfortunately, I don't think real-time usage information is available when roaming. Generally, your home provider would get notified when your device first connects to a foreign network. However, it may take a number of days for any usage details to be forwarded from that foreign network to your home provider.
To prevent unintentional data usage, you might consider enabling any Flight or Airplane modes. Those settings should disable the phone's antennae. You could selectively enable Wifi when required.
Hope this helps 😀
Cheers
