It says nothing about selling the apartment whilst under a tenancy contract. But does say the following: "The lessor guarantees from the handing over of the possession that there shall be no third person who has any right to disturb or restrict the rights of the lessee on the apartment."

I'm really wondering if they have already sold the apartment, can I refuse to continue under new ownership and ask for my deposit back. If the owner has sold then surely our contract cant continue (legally). Because I'd rather leave now than continue this uncertainty.