Advice please !! problem with rental and landlord.

I moved to Belgium in March 2015 and I find my flat on immoweb it's based in the cut of Bruxelles and it's expensive .

Anyway I paid the landlord cash upon moving in 2 months deposit plus 1 month rent .

And the landlord failed to fix things when it's due , so I told them I will hold on to the deposit until everything is sorted and he's son came back and told me anyway you never paid any deposit after providing all the receipt the father claim I never gave him a penny .

So I have them notice for 2 months and I am moving out then they came back saying they find the money just because I said I was seeking legal advice

Obviously this people's aren't serious so under Belgian law is it ok to give 2 months notice ?
By the was I stopped paying my rent since they have my deposit and I will not be dealing with such people again .
Thank you for your answer