Hello,
I'm sorry about the problem you are having. I just read through the instruction manual for your device and discovered that this recorder has only flash based internal memory, which is not recoverable. Flash based memory does not mirror files nor does it create ghost images so unfortunately, once you delete a file or folder, it is gone and will not be able to be recovered. I'm not sure how familiar you are with computer stuff but this is essentially the same as a flash drive. I'm sorry to give you bad news but I don't want you to get swindled by anyone claiming the impossible.
I strongly recommend you begin backing up your files DAILY on your computer, external drive, NAS or web storage service.