How to cancel month to month contract

Hello, I am awfully sorry but my German is terrible. I am currently on a month rolling contract and am trying to cancel this as the service in my area is incredibly poor. Every link on the help forum just takes me back to the main help center site so I cannot even look at my tariff anywhere? Is this how it is supposed to work? I also cannot register on the app as it tries to send a text to my mobile number but it is being used in an LTE router and as such, I do not receive any texts to it so I cannot access my tariff/contract details anywhere or manage it in any way.

I thank you for the help.
Edit o2_Bianca: Moved from Mobilfunk Vertrag&Tarife to English o2 Community Mobile