Something similar happened to me. In my case, AirBnB modified my 3 month booking without my consent. They just altered the booking to two months leaving me with three weeks to rebook the 3rd month. When I call AirBnB, no one takes responsibility. They say that some "ambassador" modified it but they can't tell who that is. They just give me the platitude that they "understand" and are "sorry."
Honestly, I can't operate in that environment and delisted my long term listing if they allow guest to block out months of my listing and let them cut it short when they want. It's a horrible business model.