I am happy to report that the SC resolved the issue and I received a new upgrade agreement with the correct price of $1500 today. One thing I'd like to note, for all the complaints that I may have had over the years, there isn't a time I can think of where I was not eventually satisfied with the final outcome. I am a happy Tesla customer.
So here is what happened, I think. Let this serve as a warning to others. Somehow, Tesla got it into their head/system that I had an Auto Pilot 2.0 computer. I was on a chat with Tesla and they told me that this is why it was $1800. They pointed to the page and said that it doesn't say hardware, it says computer: "This upgrade is available for $2,000 plus applicable tax, including installation, for vehicles equipped with Autopilot Computer 2.0 or 2.5 and for $1,500 plus applicable tax, including installation, for all other vehicles." They said that that my SC actually had a lower price than it should have been, that it should have been $2000.