I couldn´t find it too, and i also want to ask if anyone else having that (aparently) old problem that while we are in a call, if we use the keyboard to change directions (like calling to a callcenter), the keyboard do not work. Can't solve this problem, at all. Even tried to reset smartphone, the first thing i did after reset was trying call again, problem persists.
I have the same issue, it is very disappointing. I don't know if this is related to network carrier settings or to Samsung phone software setting
I am also having this issue. It is new. I got my phone in April and the DTMF tones worked fine. Today, they are not working. I looked in Settings -> Other Call Settings. I have no DTMF settings there. I search all settings for dtmf and DTMF and I get nothing. I don't know if it was an update or an app that caused the change. It seems crazy that an app would knock out phone settings, though.