Was the work carried out by an authorised Samsung Service Centre ? @Tgard
If so and if this issue is happening everywhere and even another networks sim card isn't connecting and your sim card is working fine in another phone [ this is all a process of elimination ] then I'd suggest to take the phone back to have a diagnostic test ran.
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
