No damages but my agency is not giving me back my deposit

What was the form of the warranty? You gave them cash, just like this, with receipt?

When they write you that they send 491€, there should be a reason. If not, did you ask them why they did not send the whole warranty? It just make no sense.

If I understand it well, they counted you only part of february (17 days - 228.62+52.76€), which you did not pay, they billed "indemnité de rupture" (legally, 3 months in the 1st year - 2 months in the second, 1 month in the 3d) of 3x390€ = 1170€, and deducted the Korfina warranty they already received of 960€.

228.62+52.76+1170-960 = 491.38 that they calculated you owe them.

The duration is 18 months, and I paid 18 months (including the 90€ per month for the chauffage....). I sent them the letter saying that I was ending the contract on its normal date of ending (3rd of May) and they told me that "to help me, they would had organized the état de lieux de sortie in advance". I asked them multiple times if that meant that I would had got my full deposit back, and they have always said yes. So, at the end, I paid the whole period, but I staid there even less, but in my resignation letter I gave them 3 months of advice, I did everything by contract...

I have been there 15 months, but I paid 18. I sent them the last payment of the last 3 months in January because I am travelling: I spent 1 month in Nepal and I am going to be in Jordan for two months in the middle of the desert, as you may imagine it's quite difficult to find a wifi in those locations. When they received that payment, as I had previously told them that I was desperate of living in Charleroi after they set my door on fire and a weird guy started chasing me in the street several times, they told me that they wanted to give me the possibility of leaving the house before with no issue. But still, I paid 18 months, and in my preavis of 3 months that they received on the 18th of January I wrote that I was ending the contract regularly on the 3rd of May. I am afraid they are just REALLY bad in maths, because I used to pay the rent almost 1 month before (I normally received my salary on the 10th of the month, so I entered at the beginning of November (I paid November when I got the keys in the agency) and around the 10th of the same month I paid December, with the result that in June they were asking me for the rent that I had already paid twenty days before. If they missed a month, would it explain all this? It would be like VERY stupid....