The warning shows that an input from the transaction has been used in a separate transaction. Did you attempt using inputs of the unconfirmed transaction in another different transaction?
If inputs from the transaction has been used, RBF would not help, except you change the inputs and exclude the ones which have been spent.
Try checking your address on the explorer to confirm if the funds are still on your wallet
None of the inputs were spent in another transaction. It is just a simple case of Blockchain.info giving incorrect error messages.
If you were to push the raw transaction manually, you'll realize that it'll throw an error saying that the fee is too low. It's due to their mempool being full and thus raising the mempool fees. That's all.