Open the dialer and dial *#0011# and it'll open Service Mode. There you can verify which bands are currently active while the phone is connected to LTE.
Don't believe anything Jazz or any of the telcos tell you about CA or VoLTE support. They're just given a list of phones that have been tested by their own teams, and if they're approached by someone who isn't using one of those phones, they will tell you it's incompatible.
Go a few pages back in this thread and you'll see screenshots shared by me and
@shaheerk for Jazz and Zong 4G+ speedtests. On a good day with good signal quality, it's not difficult to hit 100+ Mbps on Jazz 4G+ with a phone that supports B3+B8 and 256 QAM.
On Exynos, it's quite difficult go mess around with ServiceMode because the menus are very different and many options aren't visible to most users.
If you're rooted, install this app:
Phone INFO ★SAM★ - Apps on Google Play
It uses root access to force launch certain Service Menus that aren't normally accessible through the dialer. If you find the right one, you can probably find the menu that let's you enable certain LTE bands and CA combos. No guarantee that it works and it might fuck something up and you'll then have to reflash the stock firmware again. It's a risk but if it works, at least you know the phone supports it and Samsung just disables certain combos on Korean variants.