I took the time and sent a long email to 1kvoice with the timeline of all my transactions, interactions with United, contact attempts, and copies of all receipts on Friday, 9/1.
I received two receipts yesterday, 9/4 - one that was a carbon copy of the ones I already had, then a second one that was correctly priced and finally showed the $125.
No actual correspondence or apology, but I'll take what I can get.