I do not believe Tesla is doing anything. As someone that bought a car and took delivery in December 2016, I didn't even know supercharging was transferable. I bought then because of the HW2 and supercharging for life was supposedly going away (it was merely an incentive for early adopters who were paying large premiums for Tesla vehicles to pay for Supercharger network capital investment and capital investment in the Model 3).
Tesla then updated its policy, as other indicated, to clarify that supercharging for life was only transferable on early cars. Going forward, it was a perk only for the original owner (but for the life of their ownership).
Your misunderstanding lies in your acceptance, without confirmation from Tesla, that your vehicle would also carry the supercharging for life after a third party sale. That's on you and your recourse lies with the seller to make you whole (with money that you can use to buy supercharging). Tesla, itself, cannot be compelled to give you supercharging as their system has your car marked already as not qualifying due to a third party sale/transfer of title (that's how you have app access to your car).
The silver lining is that your car is so new that you don't qualify. At least its new! Mine is so old I and anyone else that owns it gets some free electrons to make them happy to drive a dated relic. (jk).
This is what my Tesla's page says about my car. It jives completely with
@MorrisonHiker. People that bought after the cutoff don't have the transfer language in their page. I think it explicitly says it will not transfer. So that was on the seller of your car to convey that information and on you to verify it prior to deciding on a purchase price (or purchasing that particular Tesla -- you could've gotten an earlier one like mine without this issue).
View attachment 311267