Probably a network provider issue
@Annoyed64: Can you try opening the Phone app > Tap the 3 dots in the top right > Settings > Supplementary Services > Call Forwarding > Voice Call > Make sure all options here are toggled off, especially 'Always Forward'.
I own a Galaxy S7. Your recommendation for clearing the cache on the three "Phone" apps did the trick. I did not need to clear the data (and probably thankful that I didn't have to).