Cheating software like in cars but in Telecom companies

I was in Germany and use mobile Vodafone prepay (CallYa guthaben): it's the thing when you pay online or buy somewhere 15 or 25 EUR to upload credit on phone. I uploaded new 15 EUR, so I had 18 EUR overall. If you travel outside of Germany to i.e. Italy, Slovenia, Croatia, you get sms notification that new roaming is in use since 30.5.2016, costing much less than it was, like not 22 cents but 14 cents per minute. Anyhow, just by trying to call a German number I get smashed -> "not enough credit". I checked *100# and true, 0.20 EUR. I have no reasonable explanation how I lost 17.80 EUR in 1 second from my credit. Except unless maybe the other operator not on German side but in the EU land charged roaming. But still, its quite some fee then which cannot even be. Perhaps some cheating software like in cars is operational in roaming settings :) Did anyone experience similar? It occurred to me actually twice, once in past, also in roaming situation.