Unable to connect to a carrier on roaming from Iphone 6

Hi

I have iPhone 6 and I was able to connect to a carrier while roaming however out of sudden it stopped. I can still see the list of carriers but not join to any - while selecting the manual option. Also, on automatic the phone is not connecting me to any carrier.

I put the sim card in another phone and I was able to connect to a carrier from the other phone.

I reset the settings but it did not work.

I turned off the phone and then turned it on but not working still.

Does anyone know how to fix this?

Thanks.

Mo