Shrink of Data File Hangs and Does not Complete

This database is 2014. It is in Simple recovery.
The data drive is almost full and there are 300 GB of unused space in the 3 data files. (The mdf and 2 secondary .ndf files)
Under normal circumstances, I would not perform a shrink but I need the space quickly and requesting the drive to be extended will take days.
But my attempts to shrink the secondary data file just hangs forever, never completes even after hours.
I have tried 2 methods - DBCC SHRINKFILE and also reducing the Initial Size setting in the GUI.There is nothing helpful in the Logs.
Any ideas? Thanks