Wipe doesn't wipe

I needed to clean out some confidential details from previous client "A" held on a USB stick.

So, I deleted client "A" file(s) from the USB stick, leaving clients "B" & "C" files on the stick.

Then to make sure they were properly deleted and unrecoverable I used the wiping tool from CCLean Pro.

To check they had gone I then ran RECUVA on the USB and low and behold the files were recovered?

So, I then copied the remaining clients' files; "B" & "C" to my hard drive - something I was loath to do as usually I only keep clients details on removable media as a security measure, and fully formatted the USB Stick.

I ran RECUVA Again and this time no client files were found.

So, what is the purpose of the wipe utility if files can be recovered?

Your comment welcome.

John