I believe you have slightly misinterpreted the endorsement as shown in AC61-65E. Reference FAR 61.183(d) under Eligibility Requirements.
"Receive a logbook endorsement from an authorized instructor on the fundamentals of instructing listed in 61.185 of this part appropriate to the required knowledge test"
In this case you must have the endorsement when you take the practical test (present it to the FAA inspector or DPE); however the endorsement is not required to take the FOI written exam.
Here is an FAA document from CATS:
http://www.faa.gov/training_testing/...ing_matrix.pdf. Scroll to page 7 and you will see:
"Acceptable form of authorization for Flight and Ground Instructor tests listed above:
-Requires NO instructor endorsements or other form of written authorization."
In sum, the FOI endorsement is required to be in your logbook for the practical test but not to take the written. Best of luck in passing the test this time!