"Hidden Wallet" onion site I was assigned a wallet by "Hidden Wallet" onion site - my BTC never arrived cause its a scam. I have the wallet address and proof that it was assigned to me under username and password - Can I get my bitcoins back or send from that wallet to another ?
Based on a Bitcoin address you cannot get your money back. You also need a private key for that. 

As the developer of the real HiddenWallet, which is a desktop application, not an online website I encountered this scam many times. Your money is lost, sorry about that.  

One more thing to consider is, if you were using the same password at other places, then you probably want to change it.