Company send legal notice after termination of services

I got legal notice from x company because of non fulfillment of employment bond, i have bond of three years but i have served two years of bond and spent total more then three years in company. like 2014 i joined, 2015 i signed bond and 2017 current i relieve from company. They have accepted my resign,given no due certificate, salary certificate, experience certificate but still after two months they have sent me notice of joining another company and dishonour of cheque and asking me more then 2 lacs , i have given them undated cheque during signing the bond, and now they have used my undated cheque in bank also. i have signed bond on green color legal paper having revenue stamp on it. all the things were in favour of companies side. i have not taken any training during my services. the bond was made only to send me foreign tour for marketing purpose. please suggest me, what should i do, if i have clearance of experience certificate, accepted resign and copy of no due certificate, sallary certificate.