Istore at Eastgate

I bought my iPhone 12 at Menlyn park; within 2 weeks of purchase it was freezing and overheating. I took it to istore at Eastgate as it was closer to home, they’ve been giving me run arounds in a space of 6 months as they keep booking it in and claiming there’s nothing wrong. The last time I went they said they replaced the rear backend but this phone is still overheating! How am I supposed to last years with this phone if it’s already messed up ? Truly I’m annoyed