docs: def unbind(self, instance_id: str, binding_id: str, details: UnbindDetails):
          """Unbinding the instance
          
          see openbrokerapi documentation
          
          Raises:
              ErrBindingDoesNotExist: Binding does not exist.
          """
          
          # Find the instance
          instance = self._backend.find(instance_id)
          
          # Find the binding
          binding = self._backend.find(binding_id, instance)
          if not binding.isProvisioned():
              # The binding does not exist
              raise ErrBindingDoesNotExist()
          
          # Delete the binding
          self._backend.unbind(binding)