Yes, that's what it sounds like to me. If it isn't showing up on blockchain, then it was never sent in the first place. Coins sent to your old address will, I believe, still eventually arrive in your wallet since it was an address belonging to you (and your account) ... so that's not so much of an issue as getting Bitinstant to actually send the coins you paid for. No, do not provide a different address to bitinstant - they won't send the coins to a different address, and that would really just confuse the situation. You'll just need to talk to bitinstant support, provide them with a link to the blockchain page that shows there has been no transaction, and then once they have actually sent the coins and it shows on blockchain, THEN you can address the issue with SR Support to make sure your coins will still arrive in your account even though you've since changed addresses.