Hi Phillipp,
You almost got me with this one, but it's fairly simple. In your question you're pointing at the robots.txt of your HTTP page. But it's mostly your HTTP**S **pages that are indexed and if you look at that robots.txt file it's pretty clear why these pages are indexed: https://www1.swisscom.ch/robots.txt all the pages that are indexed match with one of your Allow statements are the complete Disallow. Hopefully that provides you with the insight on how to fix your issue.