I would email the Worldperks service center, Attn: Jeff Borg - Worlderks Service Center Supervisor and in your email clearly establih the date and flight number which put you over the 75K qualification mark for Plat Elite Status.
Ask for all flights AFTER that date to be researched and after verification, credited with the 125% Plat Elite Bonus.
You should get your account reviwed and corrected within 2 weeks of the ate you send your email.
RC