The share flat where you must not live

Hello, my name is ot and I lived in Degenddorf Shareflat last semester. I went through something unfair on the spot and got into trouble with the landlord and the student living in the flat house. Now I want to talk about this, I hope you don't go through anything bad in this house, and I wish you not live here.

Actually, I lived in an apartment, and there is a German student who has managed the house for a long time
1.
I lived there from February to August and paid 435 euros per month, but I had to pay 635 euros in August. There were three people in the apartment, one went to her country in August, and I had to pay another 200 euros in August because she is not there.
I didn't know about that. The landlord and the other student didn't tell me about this. If they knew that they had to tell me, but they didn't tell me.
One day, before paying monthly fees in August, the student said he had to pay another 200 euros because of the contract.
I didn't pay the rent at first because I didn't want to pay, but I couldn't go to the apartment because the landlord locked the door. So I paid the monthly fee on Augudy 5th.

Second, the landlord didn't return the deposit to me. He said that if I want to cancel my house when I leave Germany, I have to write down my signature on the contract that I don't get a deposit. He brought his father and said his father was a witness who saw the sign.

Thank you for reading my long texts.
The adress is Hengersberger Strasse 85