Well we have paid out a big winner yesterday 19 btc, a few weeks back the OP 18. So it seems we can

The OP won 9 not 18. Sort out your math before making a fool of yourself. 9btc deposit, bet 2x, cash out 18. Which is a win of 9. You really like over exaggerating stats, don't you?
Did you ever cash out that other 20btc win? Do you have the transaction ID?