Updating a doctype table after delete not working

Hi,
I have a scenario, in Delivery Note I created a field “series_no” and looks up in doctype Base Series, in this Base Series table there is a select status field which is “Available”, “Used”, “Deleted”. When I add a new record in Delivery Note and used that series_no for example “B15-00001” it successfully update the Base Series to “Used”, but when i try to delete the record in Delivery Note, what i need is it should update the Base Series status to “Deleted”. I have used on_trash and before_delete function to handle the event of deletion but it doesn’t work. Please help. Thanks.