Thank you so much for the link - when I had asked in an AIS store if they have any sim cards that I can use in Malaysia they said no I guess the sales staff don't know about all the products their company sells even though it says I can buy in any AIS store

As to my original problem - oneplus has been of no use (keep suggesting the same things that I told them don't work). I was able to borrow a friends AIS sim today so I could make sure all the apn settings were correct - and still no success The signal shows 5 bars volte also shows and no combo of turning data roaming on or off, etc. allows me to download data (altho the up and down arrows indicate that it should be working), nor to use any call function.

The only thing that makes sense at this point is that maybe the IMEI was not supplied to AIS (or any other Thai provider) if what another poster wrote is correct or ?????
When I get home I guess I have to go back to my old phone next time I'm in Thailand. I'll be in Malaysia soon so I may try again there to see if my phone works there,