Yes, they can. The legal ability for a company to fix mistaken online prices after the fact was established early on.
If the mistake is a small one, they will often opt to skip the PR hit and let the mistake stand but they do have the legal right to fix thins.
It is much clearer with physical products. They will usually find and fix problem before a physical product ships. In most cases the give the buyer the option to choose to pay the correct price or cancel the order. With games, because the game it tied to an account, they are able to revoke your access to the game, just like they would not-ship a physical product.