You say you had MD tax withheld by your employer. But did you prepare a non-resident MD return? When you work and live in different states, you are supposed to prepare your non-resident state tax return first, then prepare the return for the state you live in. It sounds like you did not do that. You should have done that so that DE would give you credit for the tax you paid to MD.
What does the letter from DE say they want you to do? Do they want you to prepare a MD return and amend the DE return, or did they ask you to do something else? You say the letter is asking for "additional information."
AUDIT SUPPORT
TurboTax has a special phone number for help with IRS/state tax letters, which will be easier than going through regular Customer Support. At the page below, click on the blue button that says "Get Help from TurboTax Support". Then it will ask you what tax year is your letter. Then it will ask you what the letter concerns. Then it will show you the phone number during posted business hours.
https://support.turbotax.intuit.com/irs-notice/audit-support/
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
