Definition of oligopoly: Oligopoly is a market structure with a small number of firms, none of which can keep the others from having significant influence.
I can literally buy a SIM card in Europe for my phone that gives me 5 times my monthly usage for less than what I pay for a single month.The market is absolutely harmed by the lack of competition and we did it to ourselves by selling off the public spectrum and paying for the privilege to do so. The Republican party is the most anti-American party that exists in the US and they used the willingness of the religious right to follow whatever lip service they get paid to the ballot box.
Democrats are pretty terrible too, but mostly because they are naive, unwilling to get their hands dirty, and try to play by rules that are only used by them. You don't win a war with flowery words and kind gestures. You win it by eliminating your enemy and taking away any ability by them to continue the fight.