Since you are a NY resident, all your income is taxable by NY, regardless of its source.
MD can tax non-residents only on MD-sourced income. Maryland's rule is that income is "Maryland-sourced" if it is "compensation for services performed in Maryland." See this:
https://www.marylandtaxes.gov/covid/documents/TaxAlert050420-EmployerWithholdingonTeleworkers.pdf
Therefore, if you are a non-resident of MD who never physically worked in MD, your work income is not MD-sourced - and therefore not taxable by MD.
If this is your situation, and if MD will not refund the erroneous withholding, my suggestion would be that you protest in writing, rather than via a phone call.
If your protest fails and if you do wind up having to pay MD income tax, you can claim a credit on your NY return for the taxes you pay to MD on the income taxed by both states. Thus you will not be double-taxed.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
