Bad service and vehicle

Unsatisfactory service.I bought a new Isuzu bakkie about one month ago.There were a few small problems.After 2 weeks the gearbox was giving problems. I phoned the salesperson to sort out the problem.If took my bakkie to isuzu to be checked. According to the technician the diff and gearbox is faulty. How is this possible???? It is a brand new bakkie???? I am very dissapointed!!!! How can a new bakkie have these problems after only driving it for only a few weeks. Vehicle's are expensive. This is unacceptable!!!!!! Either the vehicle must be replaced or my money must be refunded. I will find better vehicle and service elsewhere.