I've gotten to the bottom of all this...
The username you provided for your Slots of Vegas account was for a a different account you'd had with the casino (that account had not been active since August of last year). With that account, there were no withdrawals to be paid.
Once I found your other account with Slots of Vegas (with the correct username), I was able to find the withdrawal and payment information: 4/30 Paid $391.5 + $12.5 Service Fee for transaction #87961160. As May 1st was an international banking holiday, I would expect you'll find the funds in your account, early next week.
Also, you'll see there is a shortfall from the withdrawal amount you requested--this is due to the bonuses you received (VEGASHERO (7 of 9999)(30 free spins) $75.00 + Free Spin non-cash credit $20.40). All bonuses are non-withdrawable and as such removed from the total withdrawal amount.
I hope this clears things up...