I think you have just added 500GB space to the LUN from storage but didn't expanded the VMFS volume.
Once your rescan process completes go to ESXi host --> Configuration --> Datastore.
Select the Datastore and go to Properties --> Increase
select the existing LUN and follow the wizard to increase datastore size. ( cross check LUN id before increase DS space)
Then watch the snapshot delete process. if you want to abort snapshot delete snapshot process then you can restart vCenter services however that's is not recommended and that would be last option to try.
wait for sometime to get snapshot process complete.
Thanks,
Haridas
Virtual Admin
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