I too have the same problem and have just spoken to a Samsung support advisor who tells me it is not the fault of the phone, it is the IVR Systems of the people who we are phoning. Has anyone else been told this?
I'm having the same issue. Its recent. It may have started when I updated to
Android 8.0. Changing the settings suggested here or verifying them doesn't help. It may also be an issue with the latest Samsung update. I have to use my cable phone now if im going to choose options with a keypad. Fix it Android, or Samsung.
What worked for me after chating with Samsung support:
Go to settings >> Apps >> 3 dots on the top right >> show system apps >> search for the phone application ( 3 applications) >> storage >> clear data.