cancel contract

hello im a student 19 living in Germany for university. i signed a contract for unlimited data last year on june for 30 euros a month .i got a call during august of last year and the caller told me since i was a loyal customer they would reduce my plan to 20 euros. Ever since then they have been charging me extra 20 euros to a contract i never signed to and i’ve lost 200 euros and will lose more till 2028 (contract i never agreed to signed to). i called them multiple times but they always just speak in german and my german is not that good.I also tried to check if they have a customer service email and i couldn’t find any. is there a solution for this im just a broke college student and this is a financial burden for me.

Edit o2_Daniela 18.04.26 moved from o2 Mobilfunk: Vertrag & Tarife to English o2 Community: Mobile