My phone got extremely hot and stopped working

I bought my Samsung S4 mini privately from a store in Four ways two years ago. Given that I never used a Samsung product before I was thrilled at how it functioned. I noticed that at times when I had multiple apps opened, the phone would heat up a bit but would cool down after a while. Took it to a SAMSUNG accredited repairs place and they found nothing wrong.My job demands my attention over social media. Recently, the phone would get extremely hot and I would have to switch it off to cool it down. Today alas, it fought a good fight but died after getting so hot, it warmed the cup of tea next to it. I do not have proof of purchase from 2 yrs ago. How can I get assistance with repairs and where can I take the handset in to be assessed. thinking of buying that Fruit model again.<br> Help !