Company is refusing to pay out vacation days and Q1 commission after I resigned.

(New York) Newbie to this subreddit, so thank you first and foremost. My company is refusing to pay me out on my commission bonus from Q1 sales. I checked my commission statement which is signed in 2017 and dated in 2017, however, it states "Commission Period" shall mean the period from 1st January 2015 to 31st December of 2015 comprising four consecutive quarters of a year each made up of three months, the first such quarter comprising the months of January, February, and March 2015.

Being that it states 2015 here does that completely negate this entire document?

Also, I work for a London based company, but I am part of the NY office.