Can my ex employer sue me

Hi, I have been working in a LLP for six months and one fine evening the HR and company's founder called me to sign first an amended employment agreement which I did and then they fired me in the same meeting by telling me that I asked the employees to leave the company, I gave wrong information to client and that I did not meet the target expectations since I am in Sales. Also, they told me another reason was that I don't participate in any team activity. I patiently said that I am willing to go no issues but what about my severance of 30 days to which they said sue us. During this time they also asked me to sign a contract stating that I won't work with any of their competitors or clients for three year to which I said I won't sign but I wrote a line on the letter that I won't sell the same services to the clients of the said company to which I had no problems on. But after almost a week they called me back asking me to delete all reference to their blog post and other things from my social profile to which I abided. During this time one client himself called me and asked me to help me find a vendor for technology, which I did through a email introduction and then the client went on to talk the same to my ex company. I received a mail stating that I was fired on the grounds of misconduct, trust breach, non performance and that I was taking Cashback from client after leaving the company. Since, I didn't had any proof of having left or termination I thought this mail served that purpose for the least. Post this, after twenty days of my leaving the company he sents me a mail with details of some client conversation saying that client is saying you did not do the said work to which I mailed saying I would be calling you and explain my side of story but he responded again stating that I should not talk to client and send him a mail explaining everything and asked me to pay the invoice amount to which I responded that the client will make the payment. then we had a telephonic call and he asked me to follow up, which I did. I tried calling the client and left him voice mail since the client wasn't picking nor responding. Then he again sent a mail two days later asking me if I am paying or the client is paying. After which I sent him a mail saying that I don't want any communication from his side as it is disturbing my mental peace and I am unable to concentrate on my current job. Moreover I have legal obligation to not talk to anyone at NetBramha or its clients.