That can explain what your are experiencing, there are 2 connections, one to the vCenter and one apparently to an ESXi server.
Do a
Disconnect-VIServer -Server * -Confirm:$false
This should close both connections. Check by displaying $global:defaultviservers again.
That variable should be empty now.
Now connect to the vCenter
Connect-VIServer -Server <your-vcenter>
When you now display $global:defaultviservers, it should return only 1 object, the vCenter one.
Now try your New-VM again. Don't forget to add the Location parameter, as Robert already mentioned.
