First up, I'm not from stakeunited or in any way associated with them.
What version of the wallet have you got? I can't see that transaction or address on the blockchain.
I think it may be possible that you sent the coins with an old wallet and so the coins went out on the old protocol. This means they would never have been received by SU. If you get the latest wallet, (4.3 I think), and recreate the whole block database, you will find that your coins are actually still in there. You can then send them to SU (who is therefore completely innocent) and they will receive them and stake them for you.