Dakisarak: Don't you guys think that GOG should admit that they have made a mistake as well, and return my $7.10 (5 dollars + tax and interest).
No.
Dakisarak: the game was removed from my account without me being refunded the money
Are you sure? Are you really sure? Have you checked your credit card statement? Have you checked for store credit on your account? Perhaps you spent it on one of the 24 other games on your account?
Anyway, either way, the lesson here is "if you think you're owed money, don't sit on it until you have no legal recourse and then start whining about it".