sir,i have worked in a private company.At the time of joining i have submitted my original provisional certificate and i have taken acknowledgement for that .In that acknowledgement there is no time frame mentioned in that and i have worked in that company for eleven months.Now i had left that company without any notice.The company has given me only offer letter and i have not signed any agreement.They did not given me appointment letter,identity card,esi,pf,payslip till now.Now they are demanding me to pay 30000 to get certificate back.Can i take action on them through legal..Anyone plz suggest me how to proceed