Originally Posted by
freecia
I'm pretty sure it isn't an IMEI whitelist since your old Samsung worked and was presumably non-Thai Samsung and 4G signal icon appears on the new phone. But IMEI whitelist is a thing some carriers do (*stares at Sprint*) which hasn't been mentioned. Can you get it to latch to a 3G connection and get data?
The settings have a 2g/3g/4g (automatic) setting but I think it doesn't have 3g only setting - but it something to try if I get another sim card here.