Avoiding payment like a **** casino

Silversandcasino is avoiding paying me my winnings that I won fair and square from their casino. There's a slot tournament which I played and won R200. Then I used that R200 to continue playing to have kore money, to my luck I won R600 plus from their Lobgy jackpot. I continued playing for more money, then I decided to withdraw R850 since I was not winning anymore. Then they send me an email declining payment of the withdrawal of those winnings claiming I used multiple bonuses. And I did not use any bonus coupon of sort , I won from a tournament and from lobby jackpot , also why would they let us play tournaments and there's many of them and we can play all of them, if upon winning they will refuse withdrawal? That is misleading , also their lobby jackpot, why let us win it if it's a free bonus . It doesn't makes any sense