How to get relieving letter without serving complete noticeperiod

Hello All, am working at XYZ company from last 3.7 years. The company sent me for 1 year onsite with 6 months contract. The contract says that i have to serve for six months notice or i have to pay for 6 months if i resign. also it says that manager can increase this notice period or asked me to complete the notice period based on the business impact. the contract also says that i have violated all the rules if i resign from onsite. am not sure what this really means. i had completed 10 months at onsite and resigned from onsite itself. i came back to India after 1 month from resignation (took 1 month due to return formalities internally) and am asking to be relieved in 2 months from the day i resigned. but my manager is saying me that he cant relieve me if i dont serve 6 months notice as i signed on the deputation contract letter. I requested my manager and HR several times and i also told them several times that i am ready to pay for remaining 4 months notice period. But still my manager forcing me to serve for 6 months so that i can get a relieving letter. but i cant serve only for 2 months since i need to relocate to other place and join a new company. i spoke many times to my management to convince them but couldnt succeed. they didnt give me another resource for knowledge transfer. when i asked for a candidate to share knowledge, they told me that they dont have a resource for it and they are recruiting from outside who will join in 2 months. my future employer doesnt need my relieving or experience letter. Now i dont have any option other than absconding but am personally not interested to do it. i feel that i didnt do any crime to abscond and also its not correct to abscond. i have my right to ask for the relieving letter. So please suggest me how to resolve this issue and how can i get my relieving letter. Thanks in advance!