That company owned pipelines and storage tanks within Germany, thus controls the flow of gas after reaching Germany.
It's also worth pointing out that there's been some evidence suggesting that, in the weeks and months leading up to the Russian invasion of the Ukraine, the "fill level" of the Russian-owned storage infrastructure within Germany was decreased, which would both be a way for Russia to attempt to leverage gas delivery against sanctions (in other words, blackmail), as well as yet another strong indication that the invasion was a deliberate Russian aggression planned well in advance.
If you're interested in more and understand German, I'd recommend the most recent episode of Lage der Nation, which talks about this at much more length: https://lagedernation.org/podcast/ldn284-ukraine-krieg-6-woc...
It's a bit more complex than that. Following the liberalization of the gas market, "discount providers" appeared who simply bought on the spot market because that is usually drastically cheaper than long-term contracts, and also the large utilities shifted parts of their purchase to spot market contracts for the same reason. For many years this worked just fine from an outside POV, and the margins on the retail gas price that the utilities made were usually large enough to account for short-term supply price hikes without having to raise new capital or retail prices. All seemed to be well.
Last year, people noticed that Gazprom's storage facilities were unusually low. Gazprom of course denied any wrongdoing, they claimed they are fulfilling their contractual obligations and that's it. Which is objectively true and as a result, no regulatory agency had any legal authority to step in.
And now, with the invasion ongoing (and for a few months prior), Gazprom still kept their long-term contracts but unlike all the prior times did not supply much on the spot market - which led to the well observed price hikes and utilities going bankrupt or out of business because their "old" strategy of simply buying on the spot market didn't work out.
The responsibility for the current situation rests to a large part on the utilities who forewent resilience (in form of more expensive long running contracts) in favor of short term profits. We dug our own and the Ukrainian's graves at the same time.
What do you expect to happen when long-term contracts get tied to spot prices? Why the hell would Gazprom willingly lower the spot prices when bulk of its sales will suffer from it?
Because that is what they have done for the last decades - the pipelines have more than enough capacity, even without NS2. They only stopped selling on the short-term market last year.
The only explanation why Gazprom was leaving that obscene mountain of money on the table is because they have been ordered to do so by Vladolf himself, so that he has leverage against Germany in the Ukraine invasion.
That being said, just to clarify: the discussions I was referencing in the GP comment suggest that Gazprom has not been acting as a good-faith rational actor, and has in fact been keeping their storage infrastructure even less full than you would expect due to high gas prices.
Yes, I merely explained how they were able to deflect the accusations of acting in bad faith for so long.
Gazprom was leaving literal billions of dollars on the table by not offering any meaningful spot contracts for months now, until the invasion began - a fact that no one could explain with anything else but war preparations, and war was seen as a ridiculous idea almost everywhere, so public discussion was simply left at "we have no idea what they are doing in Moscow".
Are there people out there who have doubts about this? Regardless of any opinions on the rationale behind it, it's very clearly something that was planned in advance. I didn't think that was something that was up for debate.