If you were never legally married you cannot file as Married Filing Joint. You can file as Single or Head of Household (if you qualify). You need to follow what the IRS stated you need to do in their letter. To change the filing status of your return, you can amend it. Amended returns must be mailed.
Do I qualify for Head of Household in 2019?
You can qualify for Head of Household if you:
If you were still legally married as of December 31, 2019 and a child lives with you, you can qualify for Head of Household under a slightly different set of rules. Read more
After you answer all the questions about yourself and your dependents at the beginning of your return, we'll let you know if your situation qualifies for Head of Household.
You can also revisit these questions by selecting My Info (online) or Personal Info (software), and then selecting Edit next to your name or your dependent's.
----------------------------------
How to amend (change or correct) a return you already filed
If you were never legally married you cannot file as Married Filing Joint. You can file as Single or Head of Household (if you qualify). You need to follow what the IRS stated you need to do in their letter. To change the filing status of your return, you can amend it. Amended returns must be mailed.
Do I qualify for Head of Household in 2019?
You can qualify for Head of Household if you:
If you were still legally married as of December 31, 2019 and a child lives with you, you can qualify for Head of Household under a slightly different set of rules. Read more
After you answer all the questions about yourself and your dependents at the beginning of your return, we'll let you know if your situation qualifies for Head of Household.
You can also revisit these questions by selecting My Info (online) or Personal Info (software), and then selecting Edit next to your name or your dependent's.
----------------------------------
How to amend (change or correct) a return you already filed
So you already filed both an original MFJ return, and then an amended return as HOH? Probably this was for 2018, since its a bit early for audits of 2019?
There isn't much you can do to prove that you are not married. You might need an attorney.
On the other hand, the IRS might be thinking you are Common Law married. This is still relevant in some states.
A common law marriage is one in which the couple lives together for a period of time and holds themselves out to friends, family and the community as "being married," but without ever going through a formal ceremony or getting a marriage license.
Please see this LINK for more information.