First thing: have you tried rebooting the phone? There's no reason a service interruption (which is what this sounds like, as phone calls also stopped working) should do this, but if it's a glitch it might be that the SMS app is not displaying the messages rather than their being gone, in which case a reboot may fix it.
You could also try just installing another SMS app (e.g. Textra) and see whether it can see them (all SMS apps use the same database, so if one has lost sync with it maybe another would be able to see it).
If they really are gone and phone is new, can you re-transfer them from your previous phone or restore them from your backup (i.e. redo whatever you did to copy them in the first place)?
If they are actually gone and you have no backup, they are gone. There are many SMS backup tools available, so if this is important to you I'd recommend using one, but it won't help with this, only in future.