Can you please answer the question in the my post above?

To answer your question you can't use this private key because in 2fa wallets there is more than one private key behind every address. There is the private key in your wallet, the private key owned by trusted coin which is the company providing the 2fa authentication service and then there is the backup private key encoded in the seed mnemonic which was displayed during the wallet creation process and which you failed to write down. You need 2 out of the 3 private keys in order to spend your bitcoins. You only have one.