Landlord not letting me leave

Hi, I am an International student. initially when i arrived in germany I signed a contract for 1 year. The landlord told after 6 months I can find replacement and leave or leave with 3 month notice.

I have 3 month notice to landlord. I have proof in chat where he agreed now he's harassing me and threatening of legal action. i have proof of chat where he agreed . is there anyway to legally approach this move. I can't afford to pay as per his demand.