Dutch Rail is owned by the state and track operator ProRail is owned by the state. So why are taxpayers getting screwed?

Dutch Rail – NS – has been an arms-length state-owned company for years. It is not a private company and it does not have any shareholders – apart from the taxpayer – to answer to.
ProRail is also an arms-length state-owned company, with no shareholders except the hapless taxpayer again.
But despite the fact they are both public companies, ProRail, the bit of the railway system which runs the actual tracks, is upping its fees to the passenger train side of the NS operation by 17%.
NS says this is unjustified and that it will take the increase to the cartel authority. After all, ProRail has a monopoly so it can do what it likes. The NS can hardly shop around for another railway track provider.
And, says the NS, if the increase goes ahead it means ticket prices will go up well at least 2.5% more than the rate of inflation.
But ProRail says the price increase is necessary to make the NS think carefully about what services it is buying in. And it wants to pass on more of the costs it makes to the public.
There is nothing the matter with making sure that public services provide value for money. But a 17% increase in fees smacks rather more of one-upmanship than doing anything for the public good.
The government wants to get more people off the roads and into public transport. So why is it allowing two of its own companies to act like greedy private firms and squeeze the taxpayer in the middle?