re: Any suggestions on getting through to the LA Dept of Motor Vehicles?

LINK ?

You can check the status of your license here and it will tell what the flag is for and if it involves the vehicle you sold. I had a similar experience personally and I sent the information in that they requested just like you did but I did get a response once the issue was resolved. I would try to find that request and resubmit everything. I am an insurance agent and we see stuff like this more than you would think.