Hello ThaNightOwl,
Welcome to the community!
When you refer to your primary line, are you referring to your Fido line? Are you having issues with using dual SIMs or roaming on your Fido line? You should note that the Fido Roam charges will incur if your phone uses services -- make or receive a call, send a text message or use data abroad. Accepting a call while abroad would likely incur roaming charges.
If you did not wish to use Fido Roam, you would need to opt-out of the feature. In doing so, any usage would be on a pay-per-use basis. You can view those rates in the link provided above. If you wished to opt-out of Fido Roam, 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.
If you are having issues with dual-SIM functionality, it would depend on the particular device you use.
On the other hand, if you are referring to roaming on your Fido line, what plan-type do you have? You should note that some plan-types do not allow for roaming (ie Basic plans). If you do have a plan capable of roaming, have you verified your phone is compatible with the local networks? You might consider contacting Fido customer service to see whether there are any roaming blocks on your line.
If your phone and plan are supported for Wifi-calling, that may be an option to receive the call. Though, your phone would need access to your Fido line. That said, it should be noted that while using Wifi for regular internet access will not incur Fido Roam charges, there seems to be some misunderstanding regarding Wifi-calling . I'm not sure how people have gotten the impression that Wifi-calling does not use the networks. However, that is not true. While the calls and messages do not transmit via cellular towers, they still use the networks via the internet gateway (see image here). The cellular towers and Wifi are merely alternate means of accessing the networks. Calls and messages would not be able to complete or get sent/received without the networks. As such, using Wifi-calling is technically using Fido services. Having said that, they have allowed certain usage to be free from additional charges. All the messages and calls received (from anywhere in the world) will be taken from a plan's voice minutes and messaging limits. As well, all Wifi-calling messages and calls made to a Canadian phone number while abroad won't incur long-distance or roaming charges (see link above).
Hope this helps š
Cheers
