Landlord not paying back the deposit fully

Hello,

Here is the summary of my problem:
From 23 March 2019 t/m 30 April 2021 I had a contract in a rental apartment ( particulier). In the first week of my stay I reported two issues to my landlord (sent him pictures in an email):
- the living room radiator ( biggest radiator of apartment) was broken, always cold but its meter was counting.
- he delivered me a dirty apartment

For 25 months he never fixed the radiator, while I was paying fully for the heating costs etc. He also increased the rent in July 2020 without fixing the issue. I survived the cold seasons with my electric portable heater which caused some extra electricity bills for me even. He even sent a mechanic after more than a year and the mechanic confirmed that the radiator has a big issue and should be fixed by them, but eventually this never happened.

Now that I left the apartment and made it a way cleaner than how I got it from him, he does not return 270 euros ( out of 900 euros). His reasons in email:
- 70 euros : I left the apartment on 23 April and cleaned it 3 times and returned the keys on 25 April ( final inspection day). We did not have any pre-inspection and just one week after we inspected the apartment together he has gone back himself to the apartment and re-inspected everything alone with a microscope I guess, then on 4 May he sent me an email and claimed issues like dirtiness and he wants 70 euros. He did not complain about anything on the day I returned the keys to him ( 25 April). So I never knew what the possible issues were, so I had no chance to fix them prior to final inspection if there were really some problems even.
-200 euros: he wants to put the extra heating costs caused by his broken radiator on my account while I had informed him many times to fix and he did not. With the heating energy company I contacted too and the graph clearly shows that there is an excessive amount of heat being consumed only by that broken heater. He also never fixed the broken kitchen oven for 25 months.

I have also spoken to juridisch loket 2 times and they confirmed that my landlord has no right on claiming damage or whatever after we inspected the home together as well as all additional costs caused by broken heater should be on his account and not mine.
Now since 4 May ( his last email), he keeps ignoring my emails and whatsapp msgs. He was always replying, but not anymore. I even asked him to provide me with the final settlement of heating costs for 2020 sent to him by VVE on 28 April, but he just ignores my emails and has kept 270 euros of my money for himself.

I wonder who should i ask for help to force him pay me back? incassobureaus do not help as it is not much amount of money for them, and hiring an attorney is not feasible either as they charge like 200 euros per hour. On the other hand, it also makes no sense to me that people/ landlords can easily take tenant's money if it is below 300 euros or less because simply they know incassobureaus or attorneys are not an option for tenants.
Regards,
AT