Water leakage in my kitchen and Landlord hasn’t sent anyone to fix it what can I do?

I moved into a Gewobag apartment in Berlin in May. Since the beginning, there has been constant water leaking from a kitchen valve. It fills up a large bucket every 3–4 hours, and I’ve had to pay people to come and empty it while I’m at work. It’s been over 2.5 weeks, and I’ve called at least 10 times. Every time they say, “we’ll send someone today, don’t leave the flat.” No one ever comes. I’ve heard that exact line at least 5 times.

My German is limited, but I’ve been reading out a prepared script when I call. They clearly understand it’s an emergency. Today, my neighbor (a native speaker) called on my behalf. Same answer: “We’ll send someone today.” Still nothing.

I installed my kitchen 3 weeks ago but haven’t connected the sink, dishwasher, or washing machine because of this leak. I’m now worried about water damage to my appliances and fridge. The cabinet under the sink is already getting soaked. There was slight water damage on the floor when I moved in due to this problem and I’m sure it’ll get worse now.

I’ve spent so much money renovating this flat and right now I can’t afford to pay someone privately to fix what should have been handled by the landlord from day one. I don’t like that I’m literally going to pay more utilities because of the constant water wastage.

My neighbor told me they got 3 months rent-free when they moved in years ago because the flat needed repairs. I didn’t get any rent free period, even though my kitchen has basically been unusable since I moved in.

Can I demand compensation or rent reduction? Should I join a Mieterverein or report this to a government office? Any advice is really appreciated.