Coco coir is not a suitable long-term substrate for a sav and even if you piled it deep enough, it would not suffice. A good substrate would be a soil/DG mixture, placed to a depth of at least 18".
You didn't answer my questions regarding the type of enclosure you are keeping him in or how long you've had him.
If you aren't sure of his origin, I would strongly recommend a fecal sample down to your local qualified reptile vet for an analysis. If he is indeed WC, the odds are he's heavily infested with internal parasites. If he continues to not eat and will not poop, take him down and get him prophylactically treated for internal parasites. A good vet that specializes in reptile medicine will know how to effectively treat him.