I’m always participating on Duelbits promo but I’m betting too on other sports which is not promo. So I’m sad that I experienced this even though I’m not on winning streak or on profit. 
This really sting but as I read the notification email screenshot. They are just restricting you on participating promotions that means you are not profitable for them when you participate on there promotion. Probably you made a lot of profit from there bonus while you only lose small amount on your regular be. This is the reason why they have a special line on terms that they can exclude any user without the need to explain everything. I doubt that you can get clear answer here but I’m sure it’s related on your profit when participating promotion.
Plus, if you let someone who constantly wins to keep playing, you could have them all lose money and go back to breaking even, and even worse they would go down a lot more. This is why it's paramount for them to keep those people gambling, that's why it's very very important to keep on gambling and that matters a lot, I personally believe this isn't good look for them.
But I'm leaning towards the version of a script bug. They spend thousands on promotion, and suddenly became greedy for one user using their promotions? Sound absurd. If I were you, I would contact their support and ask why you get such a special attention from them.
I am just stating scenario that I always do whenever I am playing in any gambling platform. I know many people keep their funds in the casino but I don't.
