I'm under 25, but being charged the full $110 despite being told at the beginning of filing that it would cost $15 if I am 25 or younger. How do I get the charge fixed?

I'm under 25, but being charged the full $110 despite being told at the beginning of filing that it would cost $15 if I am 25 or younger. How do I get the charge fixed? I do not want to go through the process of filling things out again.