I may have been an idiot. How do I fix this?

Trying to keep a long story short, but here goes:

On Friday, my Pixel XL decided to become a rebooting machine. After getting whatever data I could and trying everything up to and including a factory reset, I concluded it was a lost cause with some kind of hardware failure.

Luckily, I had my previous phone (a Nexus 5) lying around, and after a charge, it came back on without issues. I walked into a Sprint store and had them move my service from the Pixel XL onto the Nexus 5. No issues occurred.

I then ordered a Pixel 3a XL for my new phone and it arrived today. I went to the same store and asked them to move my service from the Nexus 5 to the Pixel3a. Trying to be efficient, I figured that whilst my service was being moved from the Nexus 5, I could factory reset it in preparation of handing it over to them to be responsibly disposed of (badly busted screen).

Problem being, I wasn't aware that the eSIM setup of the Pixel3a would require the reading of a text message to the Nexus in order to transfer service. Oops.

They sent me to another store to get the correct size SIM card but that has not worked. I can't add the new SIM card's number on [sprint.com](https://sprint.com). Their chat support said the same thing, but without a second phone to get the text, how do I fix this?