Hello M80_J,
Welcome to the community!
Sorry to hear you've incurred unexpected roaming charges. The Fido Roam charges will incur if your phone uses services -- make or receive a call, send a text message or use data abroad.
I understand you might have disabled roaming on your Fido SIM. However, you should note that disabling data and roaming data does not prevent roaming for voice and text messaging. In addition, some manufacturers might allow some data usage to occur despite those settings (see here). That's why it is also generally recommended to enable Airplane and/or Flight modes in order to prevent unintended roaming usage. You could then manually enable Wifi when required. However, those settings may apply to both SIMs, limiting the utility of the other SIM card. Unfortunately, dual-SIM functionality is not standardised. There may or may not be any way to completely disable one of the SIM cards. How the device manages dual-SIMs would be determined by the manufacturer.
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. Disabling MMS should prevent that data transfer. Though, it should further be noted that iMessages and RCS messages are sent (and received) as data and not as text messages (SMS). Even if the text message received is SMS, if your device is configured to provide Delivery and/or Read receipts, those would be sent as SMS or data and considered roaming usage.
The mobile providers only know usage. If a device is using services when its settings are set not to use them, that's an issue with the device. The mobile providers have no access to a device's settings to know what settings are enabled/disabled. If you wish to receive text messages, there is unfortunately no 100% guarantee your device won't use other services and trigger roaming charges.
Fido Roam is enabled by default on most current post-paid plans. If you did not wish to avail of the feature, you would have to opt-out of Fido Roam. In doing so, any usage would be on a pay-per-use basis. Those rates can be found here. Alternatively, if you did not wish to use any services, you would could request to have roaming blocked on your account. Though, a roaming block would also limit access to extended coverage in Canada (Fido-EXT). You would need to verify which option is applied to your account as some customers had assumed they requested a total roaming block only to find pay-per-use usage abroad (opt-out Fido Roam).
You should note the forums are community-driven and not intended as a venue for customer services. If you wished to discuss your matter and/or opt-out of Fido Roam (or apply roaming block), you would need to contact customer service.
Hope this helps 😀
Cheers
