I joined a company for a day and informed them that I will not be able to join them

I joined a company A for a day and I got a good offer from other company B, I told the company A that I won't be joining. I did not use their login credentials to log in to their system. I did not even switch on their laptop and return the company asset (laptop , charger, mouse , bag) the very next day by travelling 60kms myself. I joined the company B , but now my company A is kind of troubling and harassing me that they will sue me with 3 months notice period amount and they will put me on a "do not hire " list... Even they gave me emotional distress by asking about my family's ethics(like you come from a bad family) I couldn't take the words from them, they wanted me to feel so guilty as if I committed a theft and murder .. I informed them that I will not be able to join them as I am having continuous anxiety attacks, the anxiety attacks are due to the HRs harrasment.. seriously they harrased me alot... If a IT companies can fire a bulk of employees by taking all their access without informing them prior which is illegal as per the labour law, then why can't a innocent employee just go for a good offer.