This could need EE's intervention as much as VM's, but fundamentally if other WiFi routers work there's no reason why VM's wont.
Do other network's WiFi-calling work on this same router? I'm fairly sure the ports used for VoWiFi are standard, but the config of individual MNO's can differ - for example, EE use "mobile-preferred" as a VoWiFi default, except where individual phones allow an override. This is generally the case for Android but not iOS.
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