California says I haven't filed taxes for 2016, 2017 and 2019. I filed using Turbotax and received notification returns were accepted. How do I fix this?

You have to ask California.  Maybe they have the wrong SSN for you or added more income to your returns?

Send them signed copies of the returns plus proof of payment or the refund.

I double check the information.  And, I may do 10k of side jobs during the year, I don't change anything.  They are going after 2016 returns and now more years following.  I'm thinking there is a Turbotax bug that leaves a box unchecked or something else small.

I sent them in the 568 doc and canceled check showing payment for amount on 568, didn't work.  They kept sending me threating letters saying I owed $0.00 and penalties.  Doesn't make sense. 

I already sent them the 568 and copy of cancelled check.  Crickets.   They keep claiming I owe them $0.00 and are demanding payment and penalties.  I included a check for the requested amount and penalties based on their formula.