Your second command will only work if your OrgVdc has the same name as your Org. Otherwise you should use:
Get-Org -Name $orgs[$i] | Get-OrgVdc | Set-OrgVdc -Enabled $false
Thanks for your reply, the org and VDC are in fact the same.
Also tried the command you suggested and I still receive the same error.
I'll try RestAPI for now and see how that goes.