step 1: close all programs that may still have access to the non-existent file / folder - if necessary, also reboot
step 2: call an installed zip-program and select the 'un-erasable'
step 3: create an archive with the special option, 'delete files after compression' - this click is really important!
step 4: the zip program generally sends everything into the archive and deletes the 'un-erasable' ...
step 5: in general, the created zip archive (without compression) can then easily be deleted and appears in the recycle bin for final delete
For me it worked without any problem and maybe it can be useful for others too ...