In Germany, there is (usually) a 3 month notice for when you leave your rented apartment. Sometimes, during these months, the renter pays double rent: at the place the new apartment they're renting, and the old one.
I was told that one can get one of the rents amount back, specifically the cheaper one. Is this documented somewhere, and if yes, how can a person go about taking the money back? Is the information supposed to be filled with the tax return?