mtn Savannah mall and ombudsman

I bought a phone from mtn Savannah mall on jube 7th 2025 via contract and when I got home, the phone screen started flickering. I texted the lady that was helping me and she said I should bring it back and I did and they said it's just software updates. But the phone still gave the same problems and I returned it, they booked it for assessment and said it's system update but it still continued with the same problem.

I contacted ombudsman and ask them to help cancel the contract and they said the store wants to book it again and they booked it 3 times byt still comes back with the same problem. when I email the lady handling my case, she doesn't reply, it's been more than 3 weeks now. When I call, they keep saying she'll call you back and they're deducting every month for a defective phone that I'm not happy with. When i return it to the store asking them to cancel the contract, they threaten me with " you have to pay the full amount because it's breach of contract"