☑ Where did you get your Note20 Ultra? If from Globe or Samsung store, there shouldn't be a problem. If you got it from Smart it won't allow other network to use it. ☑ Try inserting your sim on the second slot and see if it works. If not then bring it to your service center.
update: brought my unit to a Samsung store yesterday, and after a few tweaks (including delete the entire conversation of those with unsent replies), changing the default messaging app back to Samsung's native app (was using Google's) did the trick!
update 2 i uninstalled then reinstalled Google Messages, and everything seems to work well. 🙂 A month's agony resolved in 1 action? well, dunno if my visit to Samsung yesterday somehow helped. 🙂
