I have the Samsung Fold³ @MadamBlanc and it's been exemplary to be honest.
All the features have worked well even the one's you've highlighted that unfortunately has blighted your user experience.
The internal display is stunning 👌
In regards to your issues as a process of elimination can you try your sim card in another phone and then see what happens ?
If possible try another sim card in your phone i.e Payg / PrePay.
Sometimes a sim can misbehave causing all types of issues and needs replacing via a Sim Swap by your network.
Apologies if you've already tried such troubleshooting.
The phone itself has a built-in diagnostic tool in your Samsung Members App.
A Samsung Service Centre can check out the phone too.
The Samsung Flip³ is a fantastic phone and should be enjoyed both via it's basic functions i.e calls and texts and via it's media consumption i.e videos and social media etc.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I have no affiliation with Samsung.