Uniplaces - Shady landlord not paying back security deposit

Hello. A part from all the problems and misconduct done by my landlord which I already voiced for Uniplaces, now he is not paying my security deposit. First he did not fullfil the move out date, which was supposed to be on the 30th of June and asked me for a week, to which I accepted to be flexible. Now it’s been over 2 weeks I’m still waiting for th return of my security deposit. He sent me a transfer receipt which basically never took place. As I already voiced here, he wanted to charge me an immense bill charge because he has years of unpaid bills. So, we agreed we would settle the bills at the end of the contract, and we came to the conclusion he would only return half of it (300€). We have talked several times and he is basically leading me on saying there was a problem with his account and he will fix it, but when I asked what happened he never responded. I this is utterly unacceptable, I chose Uniplaces twice due to “security” precautions, which just never happened. I lost so much money in that inhabitable place. I had to move one month earlier and paid rent twice not to be there, and now this. I demand Uniplaces is held accountable for this since I paid the service fee for nothing.