Hello @dbail,
thanks for the feedback! 
I just checked again and yes - you can cancel the contract at any time. Your regular contract period is already over and after that it is now always possible to cancel within one month! If you have sent in your notice of termination, it will all work.
And yes, I can absolutely understand that in the digital world we live in today, cancelling by letter is inconvenient. However, it is currently still one of the options and will certainly remain so. In the course of the year, however, there will also be an innovation in the process. As of now, however, the letter is a good option!
Kind regards
Jessica 