Could it be any sort of call minute reminder ?
Put the phone in Safe Mode which disables any downloaded apps and leaves the stock ones working and then see what happens.
If it stops then one or more of your apps maybe causing this @AuroraM or it's being driven by your sim card i.e a Network feature.
🌈 Stay Safe 🌈
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'm here to help. " This is the way. "