Contract 8 months old - laptop faulty

I have a contract with MTN for a laptop and a data bundle. I have been paying the contract every month since November, but my laptop (HP) is sort of an out of box failure. I starts up for about half an hour and cannot be used. Till this very day, I have not even loaded any software because of its poor performance. <br> Furthermore - the battery doesn't even last two hours. <br> I took the laptop in way back and after waiting about a month, it came back with exactly the same fault. It is now booked in for a second time for close to two months with no follow up from them or anything.<br> I am paying every month for nothing!!!!