@Simone609
Unavailable dates becoming unblocked is a long-term, known glitch in the system. You made an unfortunate error in cancelling the booking yourself, you should have contacted customer service first, but not to worry, you can still get things sorted.
Call CX. They'll most likely try to convince you that it was your error, not Airbnb's. Stand your ground and tell them you're aware that this is a known glitch. Do a search in the CC - there are lots of threads about this. Save a few of them and send them as proof to the agent you speak with if necessary, and they should unblock your dates for you. Good luck!