Rental issue in berlin for apartment

I entered in my new apartment in Berlin officially on June 15th. The apartment was extremely dirty, including multi Color paints all over the floor and in the bathroom, and a lot of things need to be fixed. Before me, an artist was living in the apartment and he/she had also cats who destroyed the floor in several places. The wood floor is damaged because of the cats. When I visited the apartment, The previous tenants were still in the apartment: so I have a video which shows the pairings they were doing and the cats in the apartment. I informed the real estate agency about the unacceptable situation and they apologised saying that they were fixing everything ASAP. After more than one and half month no one showed up or called me. I stopped paying the rent. I would like to get legal advice on next steps. I believe that the apartment was not ready for the handover to me on June 15th so the half a month I paid for the second half of June need to be discounted from next payments. At the same time they need to fix everything in the apartment. Multi Color wood floor and damaged in several places is not standard use from my standpoint. Therefore I expect that or they fix it or they decrease the rental fee.