First of all, you might have to be sure that your non- objection letter has been sent to DOS.
If sure, then you can search the processing status of your case in DOS web using your case number issued to you by DOS.
If it shows that they have not received your non- objection letter, you might have to contact them using fax. You can fax the copy of your non-objection letter to them. If they have not received your non-objection letter from CHN Embassy, the copy you fax to them will be takes as a valid evidence for them to process your case.