I used to have a legacy blockchain.info wallet which had BTC in there.
I used 17 word phrase to restore my password to this account after blockchain was updated to the new wallet.
I know that there is a tool which lets you export your blockchain.info's private keys using the recovery seed, perhaps someone can point you to it.
If I'm not mistaken, that 17 word phrase only work for restoring access to blockchain wallet
it is by no means compatible to BIP39 recovery seed, but the new bc.info wallet does have a BIP39 mnemonic seed
I think you can find your old bitcoin address in settings>preferences>Archived Bitcoin Addresses and click the show button you must see all old bitcoin addresses there ...
did you create a new whole wallet or just upgrade?
(upgrade = new 12 mnemonic seed) if simply upgraded, old wallet addresses should be there somewhere,
you can try what BitMaxz said and check all your old BTC addresses there
you need to extract one by one those private keys because legacy wallet bc.info is not HD wallet