Questions about Second Shot offer

I took and failed the 70-270 (XP) exam last Saturday and I went to sign up for the Second Shot offer, but when I tried to put the voucher number in on Prometric's web site the code wouldn't take. So I called up Microsoft and I asked them what's going on, and they said that I have to sign up for the Second Shot offer "before" I take the exam. So I am screwed now, and have to pay $125 bucks again to take the exam?
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First time I did not need the second shot. (70-290)
Second time I did big-time (70-291) - re-sit due next week
I Registered for Second Shot Online and got a voucher number.
On each occasion I've booked my exam by 'phone just in case and confirmed that I wanted to take advantage of the second shot offer.
If you should fail you can use the voucher number again as dynamik stated.