Although the allegation originated with the Ukrainian government in this article, it did so in 2013, before Yanukovych quit the Ukraine. See:
http://www.freerepublic.com/focus/f-news/3153946/posts
And every one of them knew what the price would be before the gas shipped.
They're likely to recover substantial monies if Gazprom and Russia decide to play along and admit they were charging more than necessary to make a modest profit.
But if they decide not to play, they just turn off the spigot and tell them to buy elsewhere.
It make take time to re-jigger things but BOTH parties can find alternatives.