I'm having the same problem as well. No service in Singapore. No, it's not the issue with 2G. My sim card is 4G.

found out this, using dual sim card phone. cant have both singtel and hotlink card activate simultaneously in one phone. if u need to use hotlink card, disactivate the singtel card n vice versa. gosh, i dont know whose fault is this, who to blame. cant be the phone caused previously working both activate simultaneously. another way, use yr old smartphone for hotlink card.