What should a student do when a verbally agreed on contract for a deferred examination is not honored?

First of all, apologizes ahead of time for the anonymity. I wish to protect the parties involved.

I recently applied for a deferral for an examination on the basis that a professor had accepted my deferral verbally and had stated I could write at some time during the period. (Note: our policy allows you to do this.) However, I made it clear I was uncomfortable perhaps writing this later on as I writing a test months later after the course makes me feel uneasy (personal reasons). I have this documented in writing.

Fast forward a couple months, my professor tells me in person to e-mail him a list of dates I could write after I get the deferral acceptance e-mail. I wait a little while -- and then it shows up. I reply a bit later and then everything is quiet for a week and a half and we enter exam time. No reply yet, but I wait a bit longer and begin studying for the inevitable exam.

I had been studying for nearly 5 days for this exam now (it's a course in which, I needed a lot of work in and wanted a grade as high as I could). I assumed perhaps my professor forgot and e-mailed him. It turns out, "I was too slow" and would be writing next month anyway.

This isn't what was verbally agreed on (actually, the process is the same no matter when you write and there's no officially documented deadline.. how convenient). Also, a charge is applied if you miss the "deadline". Actually, this had been agreed on for months so I'm not sure what "deadline" I could have missed.

Normally, I would approach my professor first but considering they are the one that needs to administer the test AND approve the reason, I must admit I feel some fear in that regard.

Now, I have other examinations coming up, have lost a lot of time, and have no idea what direction to head. Logically, I should continue just studying with the rest of my exams and just write at the newly allocated time.

But I would have never accepted that date so easily without careful consideration otherwise.

What's the best course of action in this case?