How can I disable FileVault Encryption Process? (Mac OS)

I enabled FileVault on my Mac (MacOS High Sierra) in the Security and Privacy System Preferences. Now my computer is extremely slow, I can't even use it.

FileVault is still in the process of encrypting my files (and will be for a very long time) and I would like to just hault the process and disable FileVault ASAP. I have tried the sudo fdesetup disable command in the Terminal many times and it just gives me the message:

FileVault was not disabled (-69573).

I am open to any suggestions on how to stop the FileVault encryption process and keep FileVault off. Thank you for your time and help!

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