Terrible MTN stores

The terrible service I get from Mtn is disgusting I took a laptop from them on contract I only used it for a month then it started giving problems I took it back so they claimed to fix it then return it which is what the did but still it came back with another problem I'm not what to do anymore because they dont want to five me a new laptop because I'm struggling with the one the claim is new, so since they took a laptop even today I never heard anything from them but they busy debiting the installment.