Can company hold resignation after giving resignation acceptance

I had resigned from the services of my company on January 3 2015 with a 90 days notice and my last working date was 2nd April 2015. While I was in notice period a fraud has been identified against my manager in last week of February. All the employees reporting to that manager was a part of the investigation including me. My laptop was deposited and scanned by IT security team on from 31st Mar to 2nd Apr '15. I was a part of face to face investigation with the case management team in my company on 31st March and 2nd April during which I gave my written statements on whatever I knew. After which my ID card was collected by HR as it was my last working day and they resignation was accepted in tool by required people. 6 days later (on 7th April) I got my resignation acceptance letter from HR team and I committed to my new organisation to join. Shockingly my organisation sent me a mail again on 9th April which said that my resignation has been put on hold and not letting me to join the new organisation and asking me to pay an amount of 1.5 lacs and then I would be released. The company is now saying that they will validate all the bills submitted by me in last 2 years which they had paid after proper approvals for team activities and team gatherings. As per the company if I want to get released immediately then I should pay back all the amount that was claimed by me which is just wrong. Now they are also targetting my 11 years gratuity. Please help.