The key thing to make much of this easier in future is to use NetApp snapdrive to manage tour windows luns. Snapdrive manages many if the things you are seeing here.
There is a disconnect between what windows sees and what the underlying ONTAP lun/volune sees without snapdrive.
What is likely here you extended the LUN probably used around 125gb, deleted some files and the shrunk the LUN in Windows, however in reality what happens is those blocks are only ever marked for deleting. At an ONTAP block level these blocks still have data in them.
The way to fix this is a space reclaim, which is something snapdrive will allow you to do, this will tell ONTAP that those blocks can be freed this will then allow you to reduce the LUN. Snapdrive helps with all that, strongly suggest you install it and will greatly simplify you LUN management.