Right, they are a monopoly until there is competition. That’s OK. You tax them higher until it becomes profitable for a competitor. That’s not ‘out of business’, just high enough.
But you can also accept the monopoly if the offer is transparent and good enough.
The colluding is a problem. It is the problem. It’s unavoidable. In every system there is corruption. This cannot be solved but has to be dealt with case by case.