Yes, you are being taken advantage of, and yes it's not fair. Guess what, nobody there gives a shit what you think. Nothing you can say will convince the company that they should stop taking advantage of you. They do not care about fairness. They do not care if you feel bad. They do not care if you cannot pay your bills. The only thing they care about is making the most amount of money off of your labor that they possibly can. Every day that you stay at that job while trying to imagine the combination of words it will take to ~convince~ them to give you a raise to the base market rate for your skillset, is a day where they are laughing their way to the bank. They have 0 incentive to pay you another dime when the current arrangement is so slanted in their favor. The only way they lose is if you have the courage to quit, and you do it quickly.
Do not talk to your boss. Do not talk to HR. Do not talk to your co-workers. Everything that needs to be said has already been said. Go on indeed, go wherever, and find a job at a different company that will pay in line with the market rate that the new hires are being hired on at. You currently have a job, and aren't desperate to leave it, so you have leverage. Then accept a position, and put in your two weeks. When you inform them you are leaving, do not entertain any counteroffers. Congratulations, in two weeks, you will have earned your ~raise~ to the base market rate. This is the only way to get what you are worth, and deep down, you know it. It's time. Leave.