-snip-The blockchain support team looked into this for weeks and I never got a clear answer on what had happened or why the address was 'used' then they closed my support ticket and I have since re opened it multiple times with them but have gotten nowhere.
Those addresses under "
used" in Bitcoin wallets are addresses that received bitcoin at least once and should belong to your HD wallet while I'm not sure if 6-8years old blockchain.info wallets are non-HD.
Anyways, the balance of 'used' addresses should reflect to your total balance but it didn't.
Based from your conversation with the customer support, specially about the xPub, it seems like it's not covered by the master public key and erroneously included to the default wallet.
From that, your wallet itself might be missing the private key for that address so I doubt that you can find the keys using the export wallet file method.
If you want to try it, here are the steps:
Note: the private keys will be displayed in "
Base58" and you wont be able to use it to other wallets, you can use brainwallet's converter to convert it to "
WIF" = Wallet Import Format (
Base58Check) to be able to import the key to another wallet.
I'd suggest you to use the offline version to be safe:
https://github.com/brainwalletX/brainwalletX.github.io | Code->Download Zip | Extract it and open index.html on an offline PC's browser.
Go to "
Converter" tab, Select "
Base58" in the 'Source Encoding' and "
B58Check" in the 'Convert to', then paste the Base58 private key to the Source text, the WIF private key will be displayed in the result.
You can import it to Electrum (
https://electrum.org/#download | verify its signature) using a new wallet option: "
Import bitcoin addresses or private keys".
That's quite a long process... but if there's no private key for the address, try to export the master private key (
xprv) instead in the backup decryption tool's button "
View JSON".
That can be imported to Electrum using these new wallet options: "
Standard->Use a master key".
Other than those, I have no other suggestion.