Hi @UrsulaP01, welcome to our forum!
I have translated your question to English as this is an International forum, please post any replies in English and it will be easier for me and other users to assist you.
You can disable data roaming if you go to Settings > More > Mobile networks and here you have a switch that you can turn off next to the text "Data roaming".
Keep in mind that the device will still roam to a different network even with this turned off, but you won't be able to use mobile data when roaming when this setting is off.
I hope that helps and have a nice weekend!
