Someone claim to have a document signed by me via docusign - which I never did

Hello,

I'm in a dispute and someone claim to have a document signed by me using docusign. They took another signed document by me and pasted my signature (with the docusign ID watermark) into another document I never signed.

Of course In my DS account there is no such document. How can I prove the document is fake? I'm a free user of docusign.

I can't prove I never sent this via email as I shared a group of documents in a drive folder, and they claim that document was inside the folder, and then removed.