Poor experience at Customer Care

I booked my Samsung S 6 edge phone in on the 24th of October. Basically after charging over night the phone hung on the start up screen. I brought the phone to be booked in at Customer Care and the the guy who was helping me, manged to switch the phone on yet in 30 min the battery dropped from 100 % to 50%. He said the phone was still within warranty and sometimes they swap it out for a new one depending on circumstances. 7 working days later as told to me I received notification to go and collect. Now with traffic it took me 30 min to get there, I sat waiting for an hr for service and then when my phone was returned to me they said they could not find anything wrong with the device and that the phone was NFF, whatever that means. Yet when myself and the person helping me looked at the test results the phone failed a few of the tests and the overall status was failed. So why call me in and waste my time and tell me there was nothing wrong with the phone. The person helping me booked the phone back in again and said they would escalate, I hope this is seen to and I wish to also have my phone delivered to me for the inconvenience!