Did SnapDrive give you any errors? Typically, when resizing a NTFS volume on a LUN we recommend using SnapDrive as it will use the native APIs from Microsoft to resize the partition and filesystem automatically.
When using FilerView or SystemManager to resize a LUN, all you have done is increase the container size (read: LUN) but not the important host-side tasks like resize the partition and filesystem. Remember, ONTAP cannot "see" inside the LUN, and since the host owns the partition and filesystem info within that LUN, you will need to extend those via the host in order to take advantage of the resize.
In Windows, typically you will run DISKPART to extend the partition and filesystem, I'm not sure if there is an additional steps for a HyperV CSV, which is why I typically recommend using SnapDrive.