I ended remembering my pin and using it.
I called customer service, but they couldn't find my AGI, either, and I had to hold for 3 hours. To anyone with the same issue who has stumbled upon my question, I would recommend requesting a transcript from the IRS or trying to remember your pin, as you'd probably have better luck with that than trying to guess your AGI. In the worst case, you can always mail in your taxes and bypass the need for a pin or AGI, but that's a pain. I also find it counterintuitive to pay taxes in the form of postage in order to pay income tax. It's just odd.
