The California Franchise Tax Board said they never received my 2018 tax return that I filed through Turbo Tax, yet they cashed my check.

[Karentaxes]

Why am I getting a notice when I paid?

[xmasbaby0]

If you have the cancelled check then contact them and see what they want from you--maybe providing a front and back copy of the cancelled check will clear it up.

[SteamTrain]

Definitely call them and check to see what they want....It's possible that they did credit you the payment, but maybe they want you to send them paper copies of your 2018 CA tax return. 

What might have happened is that you e-filed CA tax forms, but sent them a payment check by mail for what you owed, but you never looked back at your account to make sure your CA tax return was really accepted....if your CA tax return was rejected, then they got your money, but none of the detailed CA paperwork.   Either that or you selected CA to file by mail, but didn't realize that YOU have to print out the CA forms and mail them in yourself....

..or maybe they credited the payment to the wrong year?

[Carl]

Filing your tax return and paying your taxes are two physically separate things. You may have paid your taxes as evidenced by having a cancelled check. But that does not mean you successfully filed your tax return. If you e-filed, check the status of that e-filed return. ( don't know how to do that with a state return)

More than likely there was a problem with your e-filed return and it was rejected by the state. If that's the case, then you have to choice but to print, sign and mail your 2018 state return now. (You can not e-file a prior year tax return.)