Why didn't you request your game play logs?
If you really believed you were ripped off there are ways to find this out. Yet, you just let it go? Ok.....well, there is normally a reasonable explanation for everything and I highly doubt this casino is going steal a small balance.
This is the internet and I'm not saying you did this, but people have been known to play drunk, then the next day not quite remember what happened to their money. Also, you tried to cash out non cashable money, perhaps? What about the possibility that you made playthru on a bonus, which was removed from your balance? The logs will track your balances all the way down to your last play. I'm sure Nicolas would be happy to order them for you, rather than accuse his casino of stealing. I'm certain if this is a legitimate complaint they will help you resolve it. You could also get a 3rd party involved, aka, PAB.