Rolled out VoLTE in major city does not mean that it is available out of the cities.
At east coast I would suspect that the tower one pick up is not considered part of a city.
However, I believe it is more due to a contract limitation than VoLTE not available.
As for able to call previously, could it be IndoSat had the incorrect setting hence 'accidentally' permitted VoLTE when they are not supposed to ? I guess we will never know, but that is a possibility.
When they say they started shutting down 3G in 2022, the key word here is started.
Who knows when they finish ?
There are also countries that shut down 3G before 2G, due to large number of industry IoT devices using 2G, as much as that sounds strange.