Enable Auto cancel like Sales Purchase and invoice, Inventory . This module it will allow you cancel sale,purchase,accounting,Inventory even if it already done.
Cancel sales Order app is helpful plugin to cancel processed sale order. Cancellation of sale order includes operations like cancel Invoice, Cancel Delivery Order, Cancel paid Invoice, Unreconcile Payment, Cancel processed delivery order/ cancel processed picking.
This app allow you to create service level agreements and print and send your customer by agreeing SLA level.