Incentive as Additional Income
Incentive is an additional income or monetary compensation payable to an employee based on their extra work over and above the normal work as per the Incentive Scheme in vogue. Therefore, it is an additional remuneration under the terms of employment as classified in clause (c) of Sec.2(vi) of the Payment of Wages Act, 1936, defining the term "wages." As such, equity and logic demand its disbursement by the employer to the employee as soon as it becomes payable.
Termination and Incentive Payment
The likely termination of the contract of employment at the instance of the employee serving the notice period following their proposed resignation, or actual termination of the employment on resignation, are irrelevant reasons or extraneous considerations for its denial. If it is the policy of the organization, it would not stand the test of law. Therefore, if you are a "workman" as per Sec.2(s) of the Industrial Disputes Act, 1947, you can file a claim under section 33C(2) of the Act before the Labour Court having jurisdiction.
However, your statement that you did not receive it continuously for six years seems to be unusual and unexplained.