The H3 was late for Hi13 as well, and newer Hi12 with H3 support could not start before the tech was ready. There is always a line, a date , if you buy before, you get the old version. There is no way around that line. It could be even within a week or a day.
If you knew how H3 would not be supported by older Hi12, you might have waited.
Now you probably have to sell the old one, or see if replacing the Hi12 screen is cheaper, which I doubt. Selling your old Hi12 will cost you some time if you succeed and cost you some financial loss.
They have not upgraded enough of the Hi12 to change model name. Just as when they upgraded the CPU-GPU to a minor upgrade perhaps.
Sorry about your bad luck in this case.
The probability is high after a few months improved Chuwi devices with same price replace older builds. This is a continuing thing.
Do you need the H3 for some specific use-cases? A number of Hi13+H3 users have jitter and difficulty using the pressure sensitivity.
Do you have H1? Do you have such difficulties? You might not notice the difference for you use cases. You might not even have jitter.