Hi!
You can use your booked package in Germany and in all European Countries, but not outside the EU. Switzerland is not a member of the EU and therefor you have to pay for using internet / SMS and or calls (outgoing and incoming)
You can find more informations here: https://www.o2-freikarte.de/prepaid-ausland/
Or in the price list for o2 Prepaid customers (section Roaming): https://www.o2online.de/service/downloads/preislisten/
edit: For using internet outside Germany, you should check the APN setting. Valid entries are internet or (prefered) pinternet.interkom.de
Don`t forget to enable Roaming in your phone.
If necessary, try a manual network search and try to use different networks.