Can't delete time machine backups - error 8072 I am not able to delete permanently time machine backups from an external hard drive which are now in my trash. After an hour or so « deleting items » and a growing number, I get « the operation can’t be completed because an unexpected error occurred error code -8072 ». I have tried many times and different backups but no success.
I can’t even restore them out of the trash anymore and have therefore not managed to free any space from my hard drive which was the aim.

Here is what I have done :
-deleted some backups directly via finder
-stopped auto backups from time machine to avoid interference
-tried emptying the trash or « delete immediately » individually 

Any help would be appreciated, have tried looking around but no luck so far.

MacBook Air (13-inch mid 2011)
macOS Sierra 10.12.6
Unfortunately, because of how Apple has secured the system files, you'll have to erase/reformat the external hard drive (using disk utility or similar apps).

Otherwise, it will literally never delete. I've tried doing the same thing with terminal and finder, and apple won't delete the files.