Take the HDD out of the enclosure and plug directly into the main board. See if you can access it then. It looks like your only route is professional data recovery like uFlysoft: Step 1. Launch the software to scan the device where your files deleted Step 2: Preview the scan result files and make mark if it is the one you find Step 3: Recover files
Here are detailed steps for you to rescue your contents there: 1). Do not overwrite this USB flash drive in case of real data loss problems. 2). Scan it with data recovery software to see whether all of your wanted contents inside this drive could be restored. There are always many data recovery tools online. Just select one for your USB flash drive, like uFlysoft, iCare Data Recovery Free, 4Card Recovery and TestDisk, etc. 3). Save and back up all restored data on a different drive in case of data loss. Never forget to make data backup again in the future.