Overheating phone from Ackermans

I bought a phone at Ackermans and it is overheating but they are refusing to refund or exchange for another phone. They had me sit in the store for about 4 hours telling me I should prove that the phone is overheating whereas at that point I had already stopped using the phone. I made purchase the evening before then returned in the next afternoon, which was unfair as I couldn't prove the overheating without the apps I use on a daily.