In your phones connection settings go into there and manually choose another network and then re choose your own network as this should refresh the network connection.
Does this issue happen everywhere or in one place ?
Is this intermittent or does the phone show no service all the time and everywhere you go ?
Your own process of elimination has helped to rule out a sim card issue.
If this continues then seek support from a Samsung Experience Store / Samsung Service Centre.
Daily Driver > Samsung Galaxy s²³ Ultra 512Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
