Proceed legally towards aannemer?

I was doing renovations in my apartment since February 2023, they had to finish in March 2023 in theory but they were delayed. I know this is normal, and they kept working so at the beginning it was fine. Until the end of April they came regularly more or less on the days they said, but since April they canceled at least 10 times the appointments in my apartment (sometimes I would only find out when I would get back home from work and notice nothing was done, they didn't notify me). The last time I heard from my aannemer was on 16-Jun-23 to cancel once again an appointment. After that, he stopped reading my messages or answering my calls. His colleague in charge of the emails also didn't reply to any emails. I had the feeling he was ignoring me on purpose so on the 27-Jun-23 I called my aannemer from a different phone number that he didn't know and he picked up the phone. I identified myself as "Maria" but he didn't say anything and after a few seconds he hung up. I haven't heard anything from him or his colleague since then. I can only assume they will never finish the works but I have paid for more than what has been done. There is a signed contract and some factuurs with my bank statements proving what I have paid. What's the best way to move forward? I know I need a lawyer but I don't know where to find someone with experience in these topics. I also don't know if I should send another email to them to estate that they are breaking the contract and asking them to send me the money back from what not has been done. I'm not doing anything because I don't want to do anything that could be used against me. I would like advice on this.