MTN Sold Me a Defective laptop and is refusing to replace the laptop.

I bought a laptop that had a non functional battery from MTN in April. I am still struggling to get them to replace a battery that costs less than R2000. I am shocked that they are fighting hard to absolve themselves of all responsibility in spite of it being obvious that they sold a defective laptop. Their legal department is trying to make sure they don't replace the laptop. This is so ********* for such a big company as MTN. They are keeping the laptop at their Morningside branch and ignoring my emails 8 months down the line.