sorry - mixed your current level with what you had before. If you are able to identify the work item you can try to delete the workitem directly. For that use transaction SWWL.
But as there is no current note in that regard and additionally I have never heard such situation I assume that somewhere an old request is still pending.
Regarding the instance ID. Did you get it from the program or is it the only one you have for the specific user? Instance ID you can retrive from spool request (e.g. in SM37 see the spool log) and try to cancel with the abap again.
Hope this helps.
Regards,
Alessandro