Shift Allowance Not Received After Numerous Reminders - Web Developer American Express Employee Review

I am an ex-employee of WebHub India team and worked in shift for 9 months. I am entitled for shift allowance and hence I informed my leaders throughout my tenure about shift allowance not credited with my monthly salary. I was promised every month that it will be sorted out but my trust was not kept and that never happened throughout my tenure. When I was serving my notice period I raised this issue again and was informed by my leaders that shift allowance will be cleared in my Full and Final Settlement. In FFS also I didn't receive my shift allowance and It was also not informed to me that shift allowance is not credited as part of FFS I received, until I saw the FFS statement. After checking the FFS I sent mail to my Leaders, HR and Payroll India team informing same on 10th March 2015. (You can check the mail trail for all the mail communications happened.) I was promised(on call) by my leader that the amount will be credited by 25th April 2015. Even this didn't happened. So, I spoke to Payroll India yesterday on call and they informed me that they received information about the shift allowance only on 17th April 2015 and as the cut-off date was 14th April 2015 hence they could not process in April's payroll. Now the dues will now be credited in May's payroll. I sent my first mail after checking FFS statement to my leaders on 10th March 2015. I am finding very hard to understand why this took so long to process even when this is known that the amount is pending for more than a year. And, Now I cannot wait for another payroll for my payout as I have some commitments and also I am not able to trust that this will be done in May as well. I am stressed as this was never expected from such a large and reputed organisation.