API not deleting attachments

Hi all, hoping someone may be able to assist.

Am using a pipeline to remove attachments using the format of 'fid_14=&delfile_fid_14=1'

The result of this is that whilst the attachment looks to be removed from the form, it still is actually being stored (app file manager shows the attachments still exist).

Has anyone else encountered this or possibly have a solution ?

Cheers in advance.