Many here on the forum recommending that it should be in the form of a letter, via U.S.P.S.
Some have had luck getting a late removed over the phone. Many have with the letter method.
In all honesty, I've never tried the mail approach, and my one and only 1 phone GW didnt work.

It was with Cap1.
Perhaps others will chime in on their preferred method.
Are you still in OK? I'm in the Dallas/Ft.Worth area.