Frontier Airlines Lost car seats and now won't reimburse Dallas Texas

We flew into Dallas at 11 PM two weeks ago and Frontier Airlines had lost our car seats. They had a few spare ones, but didn't have anything small enough for my 2 year old so we were stuck at the airport. The entire time the lady was trying to get us to use a booster seat for a 2 year old, and couldn't quite understand why I was mad (I was really mad.)

Their only solution was for me to leave my wife (4 months pregnant) and 3 kids at the airport alone at 1 in morning to buy a car seat. Which I reluctantly did because they provided no other solution.

We were told a manager would call us the next day to make things right and that we would be reimbursed for the car seat. Its now been two weeks and we haven't gotten a call. I've called and left a messages at the DFW office everyday, spoken to the national office multiple times, and emailed the receipt for the car seat multiple times; we still haven't heard from anyone at the airline.