Western digital hard drive lost memory when formatted

hi can anyone help my western digital has gone from 2tb to 865gb when I formatted it is there anyway of restoring it to 2tb as I have tried to format it a few times and still gives me 865gb I would appreciate any help to repair this hard drive to its original 2tb

Hello,

You may try writing zeroes using WD DLG.

Data Lifeguard Diagnostic for Windows