Check at least one of the big 3 credit reporting agencies to see if the debt shows on your official report. If you are disputing it you will need to contact them to have it removed. https://www.annualcreditreport.com/generalQuestions.action
Don't respond to a phone debt collection except to get their name and authorization info. Many scams use this as a way to get personal information from you. Work through the credit agency / Know what statutory limits there are on unsecured debt in your state.
Disclaimer: Not a tax professional. Information gathered from internet links. Anything dated in June 2019 was posted in prior years and is before the 2019 limits and changes.