best is, they say my phone was 4G and VoLTE compatible (worked on Simba) last year, but this year it does not work because it degraded to 3G.

ask to escalate, say cannot, claim got no system to log in cases, track. (rubbish answer, because they
do have issue tracking system)
claim can only call internal staff on personal basis, and therefore they cannot reveal number to me. Hence, no way for me to follow up, or for them to contact me with updates.
ask to speak to a technical manager, (i was at Kaki Bukit), they say, not available, all interactions must go thru them.
ok, simba is not the only game in town.
strike 1: local network cui.
strike 2: drop support (phone shows it is on LTE voice network, but they dun want to register it on IMS)
strike 3: simba voice app deprecated (but still works if already installed, but dunno when it won't work anymore ie no more server<-->app connection)
attempt 4: let's see how the roaming and voice app works during my next few months of travel. if this fails, then bye-bye simba for 3rd and last time.