Extra service charged

Hello I changed my pre-paid o2 sim card for a contract last month, and I received my first bill a few days ago. Now I see that the operator that helped me with my contract, may have made a mistake. I am charged an extra my monthly unlimited plan although my contract is 6GB. I checked my sms and see that this was activated and deactivated on the exact same moment that I was signing the contract at O2 shop, which points to the fact that this indeed might be an operator error.
Can you please check and see what’s up with that?
I tried to call the hotline but I don’t know what to do because it’s just talking in German and never connects to an operator so I can ask to connect me to an English speaking person.