I'm guessing what might be happening is that you have a v2 license. That license was valid for the v3 betas, but is not valid for the v3 release. That's why you've been able to use the v3 betas for 4 years without being asked for an upgrade fee, but now are.
Many people bought keys after the v3 beta started, and those keys are actual v3 keys so they don't need to pay for an upgrade.
All of this was announced when the v3 beta started. It seems to me that the biggest thing that 'changed' was that the v3 beta had such a long duration. My recollection is that it was supposed to be something on the order of a year, and it ended up being more than 4 years. One way to look at that is that the v2 licenses were useful for much longer than they were supposed to be. I'm not sure it's reasonable to complain that "I was able to use my v2 license for 4 years instead of only 1 year before being asked to pay for an upgrade".
On the other hand it might be reasonable to complain that while v3 was in beta there were no (or few?) bug fixes for v2. But that's different than being asked to pay for v3.
All that said - I have a v2 license and my install of build 3143 isn't demanding anything. It does say "(LICENSE UPGRADE REQUIRED)" in the title bar - that's all. I don't know if there's a time bomb that will cause it to stop actually working at some point and require an upgraded license key. This is on Windows in case the behavior is different on Linux.