Tempest Carhire ******* - paid more than double the quote received.

Hired a car in Cape Town and booked the car with Tempest Carhire through Kulula, as was quoted a Discovery Vitality discount. Tempest Carhire than invoiced me after I returned the car, more than double I was quoted and it has been a nightmare trying to get Tempest to explain why I ended up paying this amount. Eventually Tempest advised that it was because I took the car 30 minutes before the scheduled time! I certainly am not accepting this as a reason and would like someone more senior from Tempest to sort this out and provide a refund. Every time I phone the manager (Craig) has been busy and could not take my call. Kulula have been trying to assist to get this sorted out, but I will never hire a car from Tempest Carhire again!!