@Sven35
If you cancel a long term stay reservation, then you have to leave on date of cancellation.
(allthough still max 30 nights need to be paid, as mentioned in the long term stay cancellation policy).
If you want to stay 30 nigths of reservation booked for longer time period, then ask the host if he/she is willing to shorten the reservation to 30 nighs (and not charging you another 30 nights because of the policy).