I understand your frustration, and I get that you don't buy their inventory reason. Just like you are entitled to your own opinion. I was frustrated too, but given how it's a free contest, great I won. Any prize won is something I didn't have before so I'm not gong to cry over it.
Anker host numerous competition throughout the year, and based off their customer service I will say they did not try to dupe people. They are always going out of their way to make sure the customers are satisfied and happy.
Inventory is a very logical reason, you may not think so, but given how many places this contest was open to it it is understandable. You may have stock in the US, but not enough for France or the UK or wherever else so you cannot ship some people one batterypack and others a different one, so to remain fair to everyone they changed it to one that has adequate stock across all warehouses. They may not have anticipated so many people from one location winning, hence why stock is in short supply for that area. And just because they are still selling it doesn't mean that Amazon is out of stock because while it comes from Anker it's shipped from Amazons warehouse.
You can hate on it all you want, but please spare your conspiracy theory and bashing of a company because they do far more for communities and the people than most other companies and go out of their way to try and keep everyone happy. But at the end of the day you can't please everyone, and they reserve the right to final explanation and thought.