It's very possible that they may have it but just not started reviewing/processing it yet. Until they do, you won't find it in their system when you try to track it. Allow them a couple more weeks and then call them. Mailed returns always take a bit longer to get entered in. If you have to ever mail one again, you may want to consider using a tracking service with USPS or maybe FedEx so that you know once they receive it.
This was done 10 months ago and was not accepted by the state because of an error that I corrected. But now I can’t proceed any further. I am sure all that is left is to sign and file. How do I go farther?