Hi @tenmen
Is this happening everywhere or in a particular area ?
Try your sim card in another phone as a process of elimination.
Also in your phone's settings, General Management, Reset , reset network settings.
Your phone has an internal diagnostic tool in your Samsung Members App under GetHelp.
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. "
