Roughly a month ago, a Telekom operator visited me. I thought he just came for a routine check, but it turns out I actually signed a new contract, making me change the WiFi provider. I am still learning German and I couldn't understand everything, so I admit it was my fault for not reading the contract and not knowing what I was signing.

This happened rougly a month ago and I forgot to cancel the procedure because I've been very busy with other things, but today I received the package with the new router, which reminded me of of the new contract. 

The contract should start on the 1st of April, is there any way for me to cancel the contract before that date?