CSS Corp Private Limited - Biased and Unfair Treatment Arbitration Defamation of Character

It has been almost * months since I have joined with CSS Corp and I was tested positive for COVID-** on **th of July **** and was on medical leave and today I received a call from my BHR stating that my previous employer details are fake whereas no such company exist, and they are demanding a confirmation mail from my previous HR Manager to whom I don’t report to anymore but I would like to know how and why did they come to a conclusion as such. I worked for a company which is registered/Incorporated in the year ****, and just as I raised complaint against my superiors for the ill treatment and to get leave for COVID-** Treatment, which I got and I am supposed to rejoin on **/**/**** but now my previous employer details are fake as per the current employer. This is completely absurd and unprofessional. Just giving a call and stating after * months stating background verification check failure as the previous employer doesn’t exist and I did share them the address and information of the company and now they need an email from the HR of the company to state its true and they are not fake, Isn’t this Nepotism.