Disappointing service from Apple for iPhone!

I only use Apple products including iPad, iPod, iPhone XR, iPhone 6s, 5s etc etc. I recently had a problem with my iPhone 6s and was told it was a software and or hardware issue and could not be restored or repaired despite attempts to wipe, restore etc to then be told it could not be fixed. This to me is clearly an Apple product software/hardware failure problem. I am extremely disappointed as there was nothing wrong with the phone and now it cannot be repaired. If this is the case I will be very hesitant about purchasing another Apple product in future. I would therefore like a reason as to why this has occurred and the phone cannot be restored or repaired regardless of how old the phone is.