AI is certainly prolific in writing diatribes!
Samsung blocks VoLTE on all Samsung devices that do not have their stock firmware, this has been true for some time, and is noted in our official devices page: iodéOS official supported devices - iodé So in this case you should contact our support email to request a device return / exchange.
To Sunrise configuration, please see this writeup that solves the issues (but again your issue is having a non-VoLTE capable device and a carrier that has discontinued 3G calls I think).