DTMF tones not working in roaming

[Fergbot]

I live in Italy and have an Italian provider (Iliad). My Iliad plan allows unlimited calls both within Italy and when roaming within Europe.

My A72 DTMF tones work fine in Italy. I traveled by car to Austria and, the moment I crossed the border, the DTMF tones stopped working and did not work for the ret of my traveling (Germany, Switzerland). 

The moment I re-entered Italy, a few days later, the DTMF tones started working again.

Can anyone explain? I did not change any settings prior or during my trip abroad.

Thank you