Rental contract termination - Leuven

Hello, I need help/advice for a situation I have.

I'm doing a 2 months internship in KU Leuven (December and January), and before coming (29th September) I signed a student contract for a room. The landlord asked me to pay both months of rent (total of 1400) instead of taking the deposit, and so I did. He didn't use a KU Leuven Stuvo contract, but a different one.

When I arrived (1st December) I found the house super dirty and my room was still full of the stuff of the girl who lived there before, not only in the wardrobe but on every surface in the room. In the room there were also a lot of wood bugs and the heating didn't work (landlord gave me a portable heater).

I asked him to free the room and to clean the house, as in the contract he stated that I would have found a hygienic apartment, and after 5 days of asking daily and waiting while not only he didn't clean, but one day I found it even dirtier, I went to an association to get free legal advice.

They told me that since he didn't register the contract after two months of signing it I could terminate it without notice, but even if he did register it I wouldn't have to pay any fees since he wrote in the contract that I had to give "0 months notice". So I sent him the termination of contract letter as a registered letter on 7th December asking for my money back, and I moved out.

The question is: since I broke the contract after a violation on his part, how much money should I get back? I'm sure that he has to give me the second month's of rent, but what about the first? In that association they said I should get it back as well, but online I read different things so I don't know what to think.

Also I'm not sure I can afford a lawyer if he doesn't pay me back, are there any affordable options?