You should try clear combobox with method(slot) QComboBox::clear()
description clear
And then simply append all items with QComboBox::addItems
description addItems
void refreshServiceComboBox(const std::list<QString> &service) // better QStringList
{
if (!s_serviceComboBox->isVisible())
s_serviceComboBox->setVisible(true);
s_serviceComboBox->clear();
s_serviceComboBox->addItems(QList::fromStdList(service));
}