Legal Advice for renter (tenant) protection

My husband and I have moved to Brussels since March. We have rented a flat it was a good one, that's what we thought at the beginning! The flat is a duplex; the bedroom is in the basement with a small room as a seller. We discovered leakage between the cellar and the room that transmits very bad smell due to the existence of pipes in the cellar. After living there we can’t sleep because of the smell coming out of the cellar, the humidity is high and since there is no good ventilation I started to have problems with my nose. Adding to this we have found a humidifier in the house when we have rented it, which means the landlord knew previously about it. We have asked the owner to solve the problem, after two month she sent two companies to inspect and they proposed to fix the problem by adding a ventilator to enhance the air quality, and make a fixation with the pipes. She got an expensive offer, however, she called us in a very rude way and said she won’t solve it because it is expensive, or else she can but she has to increase the rent! We can’t stay in the flat anymore because my nose problems. The owner is really arrogant, and when we told her we don't want to stay, she said since we have signed a contract for three years we have to pay three month. Or we go to a lawyer. The thing is that when we signed the contract we didn't know we will have this ventilation and humidity problem, we took it as a good and a healthy flat to live in. now she don't want to solve it. Please is there any customer protection, or renter protection. Since we are expats in Brussels we need to know what our rights are. I am sure what she is doing is illegal and since she refused to fix the problem we have to leave without paying this three month, and we have rights to say that we were tricked. Where shall we seek legal advice, or what are the process to solve this problem?