Well... Trying to send coins without syncing is always prone to problems. I really don't know why you were suggested to do that in the first place.
But still, I don't think your coins are lost. Just probably the wallet software is somewhat confused. What are your addresses? You can check them both in block explorer (
https://chainz.cryptoid.info/btx/), to see if they actually have coins on them.
It is possible that your addresses contain coins, however the wallet doesn't show them, as it 'thinks' it has sent them.
In any case, I would suggest to back up the private keys of those two addresses, and then try to restore them on the new wallet - using the procedure I outlined above. If they actually have coins, you will see those coins in the new wallet.
Well they never showed up anywhere so I'll just write them off as they seem worthless, it was only 710 BTX anyway.