VOLTE gone after update, revert to Android P, EDL recovery done. Network stuck on EDGE

[supermankesu]

Please tell us some basic information before asking for help:
Model Name: ZS630KL
Firmware Version: 17.1810.2011.183
Rooted or not: Rooted
Frequency of Occurrence: Evergreen Now
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JIO volte worked flawlessly since purchase in December 2019. now no 4g/volte works, no jio no vodafone. same SIM cards working perfectly in other devices.
enhanced volte is ON, 'LTE only' in service menu too. but still stuck on EDGE/2g.
reboot, format, reflash android 9 and 10, nothing works

[Scooo]

victor0_ASUS

Hi, we suggest you to please visit the nearest ASUS service center for better assistance. Locate here : https://www.asus.com/in/support/Service-Center/India

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Please stop suggesting everyone to visit nearest Asus centers, not all live near one. You suggested me the same but I had my issue solved with the help of some fellow ZF6 users. I'm glad I didn't just listen to you straight away.

Also, please try not to post this message so early on as others who might want to help will be discouraged after noticing your message.

Thanks,
Scooo.

[supermankesu]

UPDATE:
upgraded to A11, still no volte. Fastbooted back to A9 service firmware, still no volte. Neither on Jio nor on Vodafone.
WiFi calling worked flawlessly on A10 & A11 for a while, but gone after the reboot.
taking this shitbrick to the service centre tomorrow!