Charge of $100 to change middle initial to full name

I booked a flight from Cincinnati Ohio to Cancun. They said provide name as it appears on ID or passport. I provided name as it appeared on our IDs which was with middle initial after I looked at passports they show full middle name. So I called to have them change it & they charged $100. That is ridiculous especially when instructions are deceiving if IDs & Passports can be different. We are asking for a refund of the  $100