MTN

I went to do an upgrade instore and was looking at some of the suitable devices. Anyway a sale's lady showed me a dummy hauwei p30. And persuaded me to take the device, stating its a nice phone. When i got home, i switched it on and i did not actually like the phone. I phoned mtn store and asked if i can exchange it for something with a higher package. I was told i cant do that. Its not worth paying so much for the next 2 years when im not happy with the device. I did not use the phone as yet. Is there any way i can cancel my contract with mtn? We have been with mtn for over 20 years. The least they can do is exchange the phone which is not even a day old yet.