Faulty Acer Aspire 3 on contract

I bought an Acer Aspire 3 for Telkom in contract in February. The device has been faulty ever since it came out of the box. I've sent in the device 2 times now but the manufacturer insist there's no hardware damage. The device is extremely slow and constantly freezez or goes blank. I continue to pay for a device that isn't usable.. It's the third time that I've launched a complain and I'm going through the same process of sending in the device again. I'm also unable to receive any form of assistance from telkom as non of their lines are going through.