Are you sure you have exactly 12 words? If so, I doubt those words have anything to do with blockchain.com wallet.
Blockchain.com started to use 12 word BIP39 seed phrase in 2016.
As you say you created your wallet in 2013 (which is before their upgrade), your seed phrase should include 16-17 words.
Thanks for pointing out my mistake because I just check again it's not 12 it's 18 words seed I just check again and count words now sure about these 18 words.
Now correcting in Post 1