[omouse]

How many hours of this developers time did you take up? Refunds don't exist unless you're willing to go to court and if the work was actually damaging to your company. You took a risk and you have to pay for at least the time of the developer if not their skill (since it wasn't up to your expectations).

In any case, you built the app from the scratch. The previous dev with their previous crappy code base can go cry somewhere else and stop making defamatory comments about your company.