I see. Thats strange. Then like what others mentioned have to use simba voice app. Alternatively ask simba for help since your phone is supported volte in their list.I no longer have simba physical sim card so can’t check anymore
BUT i have done everything I could. Some users’ also say must use simba voice app to make calls.
1. APN - checked
2. VoLTE settings - checked but dun have. See quote that i am attaching in this reply.