Where are you trying to withdraw the funds to? I'm thinking they ONLY allow transfers to their web wallet and then you'll have to withdraw to an address from there...
Have you checked their web wallet/maybe a dashboard overview if they have one, to see if the coins are just there?
im withdrawing to their web wallet, it is the only provided option. they say they will have it transferred within 2 days for a small fee... but it refunds me minus the fee.