I had previously made a mistake and overpaid my taxes.

I had a Notice from NY State which recalculated my taxes wrongly, and I challenged them. But I never heard back in 3 years. What are my choices here?

If it is for tax year 2012, it is probably too late to do anything.

Call the New York tax department and ASK!

It is for tax year 2013

Call tomorrow. It is the LAST day the state will probably accept any adjustments

The thing is I responded to their department notice online 3 years back. Didn't hear anything back.

Isn't 18th the final date to file BTW?

Yes, to file for 2016.

The 15th is the last day to amend or adjust the 2013 tax return, and I doubt that the New York tax department will be open on Saturday.