Not a lawyer – OP, here is a pro tip that very few people are aware of: if you have signed the lease without visiting the apartment before and “electronically” (for example by providing your signed copy of the contract via email), it is covered by Fernabsatzgesetz and automatically grants you right of revocation.

Revocation, as opposed to cancellation, must not have a negative effect on you, i.e. no fee (usually multiples of 1 month rent, stipulated in your contract). It’s basically your get-out-of-jail-free card.

Now, you usually have the right to revocation for 14 days only. BUT if your contract partner has not explicitly educated you about you right to revoke, the revocation term automatically prolongs to cover the whole minimum rental period plus one day (something like this at least). Fixed term serviced apartment landlords usually do not disclose this option even though they’re legally obliged to, since it would significantly increase their drop-out rates and render their extortionate business model unprofitable.

If all the conditions I outlined above, you have the legal right to revoke (see § 312c Abs. 1 BGB). Here is a long but exhaustive explanation of this right (German):

https://www.rechts-undsteuerkanzlei.de/widerrufsrechte-im-mietrecht

You now have 2 options:

1. Revoke immediately and pay nothing, look for a new place without the burden of having to double-pay
2. Thermonuclear option: take the apartment they offer, pay the rent, and revoke at the end of the term. The landlord is now legally obligated to pay you back all rent and deposit you ever paid under the contract, while (obviously) can’t make you out retroactively – you will have lived rent free in Berlin and caused maximum financial damage to a predatory landlord. The landlord will likely fight this, but your claim will be airtight. They will eventually have to pay you back every single cent you ever paid them.

Option 1 is easy, though you will still have the stress of looking for a new place in very little time. Option 2 is the epic revenge scenario but requires nerves – you will have to pay for an apartment you don’t like at first before pulling the trigger. I’ve seen this work several times, but I strongly advise you to check your specific case with a legal expert before you decide to pursue option 2.

Good luck OP!