Resignation letter rejected

Hello Sir, I am working in software company from last 3 years and 10 months. I have resigned from my company but my employer rejected my resignation. I was working in another company on contract with payroll of my current company. The another company offered me permanent payroll with them so I resigned from my current company in the month of July. After serving a notice period of 2 months current company requested me to retain here as there is negative impact on business and asked me to show the loyalty such a emotional blackmail. So I decided to continue at that time on condition that I will not work on contract with the same company again. After one month they are asking me to work for the same company on contract again on a different project. Then I started looking for another opportunities in the market and I got one so I resigned. I didn't signed any bond and reason they are telling me we have incremented your salary as per expectation and you will have to serve 6 months min and train minimum 6 people with the technologies and experience I gain in last 1 year. Please suggest me what I can do? Thanks,