Landlady refuses to fulfill an agreement

If it was only orally agreed to, and here is the main point, that it was to be officially done in writing, then it is invalid if the written contract never got made. It is seen as an offer to go into a contract but not a contract itself. And while in Germany one can make an oral contract - proving it is next to impossible. But so many people are always looking for rooms that maybe it would be worth it to make an effort yourself to see if you can't find someone to take your present one.

Thank you very much for your reply. Our conversation was in written form - in a chat in WhatsApp. She wrote that "we will sign a contract starting on the 1st of October". No conditions were mentioned (such as finding another renter). Does this mean that it is a binding agreement?

NO, it’s not a binding agreement since it is mentioning signing a contract that never got signed. The message only shows intention but is not a legal document. I've made many agreements business-wise and then the people don't send the contract back signed and there is nothing one can do about it. Until one has a signature on a contract in Germany, even if all detail were agreed on, it's worthless. But I am not a lawyer, so don't take my word as legal advice.

You can of course go to a lawyer and waste lots of money and for what? Taking things to court in Germany can takes years and the court costs alone can be thousands of Euros and even if you win, they might make you pay part of it, and possible all if you lose.

It might seem annoying but you were at most mislead into thinking you could get something cheaper. But most important, you have a roof over your head. And maybe you can switch to a cheaper room once the landlord has found someone. Or you can look for a completely different place if you like. It’s your decision but it sounds like you are making a major problem out of a minor one.

Thank you, TominStuttgart!

Legally the situation is like this:
You have a valid rental contract for your current apartment. If you want to change that unilatterally, you need to terminate it with the notice period agreed on (and with no guarantee that you will get another contract).
Everything else would need a mutual agreement between you and the landlord. In your case, she clearly does not agree (any more) to the change you want. You cannot force her to agree (again), unless you can prove that a valid contract was alredy agreed on. I don't think the conversation you mentioned can be seen as contract - but you are free to consult a (costly) lawyer to see if he/she sees this differently.

Thank you, beppi!