Offer letter not signed still company is forcing to take resignation

I had an offer from an IT company to join there, I was not sure to join but the HR team forced me to come at least for discussion on the day of joining. I told them that I have objection on the Employee Termination clause mentioned in the offer letter, they agreed to change it meanwhile they forced me to sign PF, non-disclosure agreement and Personal Information form of the company which is printed text on A4 paper, I didn't sign any offer letter (which has the mention of notice period, termination by company or separation by employee) that day and not even taken any company asset as they told it will take time to get the terms changed having changed notice period and termination condition, so they send me revised offer letter next day, I thanked them for the changes and next day replied that I cannot join as I am going to join some other company. Now the HR is saying that I am their employee and I have to take the laptop and resign then only I can go anywhere else. What should I do?