Query about bond with my shipping company which is one sided

Good mrng sir Myself amritpal singh belong to a farmer family after completing 12 in science i had joined a shipping institute in pune at that time they promise 100% placement gurantee on their own managed ships. Fees struture was about 4.7 lakh for kne year course which was very high as compare to other inst. Which charge about 2 lakh. I completed pre study course and then my onboard training started which is need to be 18 month on ship as traniee and i had completed same during training i use to get stephen which is also very low as per other comapny. After my training i had given exam for officer which taken by dircetor of shipping india at my own expenses. Now after getting coc certificate of compentency when i really become an officer and its time for me to get earning. My company said me they will not take me as officer until i sign their bond. That bond contain that i need to sail with them as a traniee and as officer 24 month. Nothing else has mention and i fail to do i have to pay 15 lakh to them and if they donot want me they will issue notice me to free of bond .I had sailed with them 13 mnth as officer and now at home from 2 year due to some family issue am not able to join . As per bond they need to send me notice after 4 month of gap ..i had recived a notice not legal but printed by them few day back. Pls davice......