Claim of pension benefit

[Gary]

I left a company. I requested a lump sum of my benefit. The lump sum was calculated based on age nearest birthday (plan historically administered this way) at time of distribution. My age nearest birthday increased by a year prior to the distribution date. However the plan administrator paid my lump sum based on my younger age. I submitted a claim stating that I am entitled to an additional lump sum payment, since my age increased by time of distribution. Any thoughts. P.S. payment was made about 9 days after I attained my next age nearest birthday.