If you continue to pester them, they may offer you a $100 voucher (pretty worthless since it doesn't include taxes, CIC, seats, or bags, but YMMV), and if you pester them some more they may up the voucher to $300 - again fairly worthless. They could offer a $1 million voucher and it would have the same value since it can be used only once and only covers what they determine to be the actual airfare.

Using the vouchers subjects you once again to the misery of flying with Frontier.