Forcing to sign a undertaking letter

Even after my proper handing over my boss is asking me to sign a new undertaking letter with terms such as 1. I shall abide by all terms and conditions of employment post resigning whatever applicable. 2. I shall not work for M/s (xxx client company) directly or indirectly or through any contractor or any other agencies. 3. I shall not enter the premises of previous project site without written consent from relieving company . 4. I shall keep all the information confidential to relieving company and its customers. 5. I shall not provide any service to M/s (xxx client company) in any capacity for any of their projects in India or abroad. No info was given to me at the time of joining before 4 years in the relieving company. In between i was forced to sign a terms & conditions which bears that "Employee undertake not to work with any competing business of the Company for at least a period of one year without our written consent, from the date of Employee leaving the services of the Company" but now my relieving company is asking me to sign for modified unconditional undertaking & they are blackmailing to sign this in return for my pending partial salary, pf settlement, income tax settlement, relieving & experience letter Sir, please advice me how to face this & win? Thank you