issue resigning from an apartment in Munich!!!

Dear All,

I would greatly appreciate your help concerning the resignation from an apartment in Munich.

I sent my resignation letter to the landlord with a 50 days notice (it is a furnished apartment and my contract requires 30 days).

However the landlord did not accept the letter which is now back in my hands.

I experienced a similar situation in France, where my landlord played this game for 3 months to oblige me to keep paying the rent, even though I had moved out.

I think I will go directly to the authorities to get more information on what to do in these cases.

Since I do not speak German, any insight or suggestion on the matter from your side will be helpful.

Thanks in advance,
Fabiana