If you deposited money onto a website but didn't like the minimum bets and low RTP on slots, I don't understand why you deposited a few hundred dollars on this website once again, but that's in the past and doesn't require a discussion.
They have the right to make whichever minimum bet they see fit, and you can simply choose a website which offers different conditions. So while these changes with minimum bets sound shady and the support's responses are rude, it's not technically scam. Since Nitrogenbetting is owned by Nitrogensports, you can try to contact them on Bitcointalk as well.
And this is what makes the situation a bit odd where someone is fully aware with their minimum amount bet and have some bad past experiences with it then why would continue to deposit?
I dont see the point on abusing the bonus though since it does still require 30x wager requirement so its out of the possible motives.
I dont see that those set-up when it comes to minimal bets are indeed intentional and as same where Twitchyseal mentioned above this isnt something can be called a scam.
You've been aware and if they are really intending to hook up players to lose then they wouldnt really mind on giving you out some bonus or compensation.