Please message Optus Support 24/7 from the My Optus app. If you do not have access to the My Optus app you can use social media to contact Optus Support, please send a PM to Optus on Facebook or a DM on Twitter and include in the message you do not have access to the My Optus app.
From petergdownload this was marked as a Solution in another thread.
Contact Optus as above and request one be sent out. It will cost about $25. If its just stopped working (as opposed to you actually breaking it) then there should be no charge as you don't own the Fetch box and Optus are required to keep it operational (and it can't operate without the remote)