Samsung Tablet for repair since April.

I am very dissapointed in Vodacom regarding the service on my Samsung tablet. I booked my tablet, that is still under warranty in at Greenacres Port Elizabeth,with the problem that the device overheads, battery problem,flashing screen. It comes back with the same problem, I send it back for the second and the third time. Now I send it back for the fourth time with the same problem that it was send in the first time. It is at Vodacom repairs from 11th April. I pay my subscription every month for something that I dont have, I lost my data as well. I told them the third time when I booked it in that I want a new tablet or they must cancel my contract. Vodacom said it is out of their hands, Samsung must decide whether they want to change the device. I now want my data refunded as well as my subscription fee for the last two months. I am also going to the onbudsman about this problem.