Fraudulent Tax return for 202 under my social security#

I received a notice(5071C) from IRS informing me that 1040S for 2021 was filed with my social security Number and requested refund for 2021!

 

WE have files Extension with my separated husband for tax year2021 and not fantasized our taxes yet. I notified IRS immediately and filed form 14039. What other actions should I take now?

 Do I need to file 2021 tax return quickly? What obstacles will I face for filing for this year? Although the CPA filed the extension as Married filing Jointly, I intend to file as Married filing Separately due to the risky financial decisions that my separated husband made without my approval that can have severe tax consequences if we go ahead with Married filing Jointly. Any assistance from the community would be appreciated