Bad Service no responce from management

My phone (NOTE 3 - not cheap!!) was booked in (All ready more than 12 times). Every time I get the phone back and it has the same problem. Now the phone was booked in Again (after head office phoned me to try and sort out my problem) on the 8 July. I have requested a new phone since 12 times was enough times to sort out my problem or I asked to have a letter to state that the phone is irreparable so that I can take this up with my insurance - now after speaking from the 1 manager to another I still do not have answers - They also does not know where my phone is because they have phoned me to asked if I still have my phone. With all the time my phone was booked in I had to buy another phone so that I can continue and they take forever to get back every time with the same answer - Its fixed or they have replaced a motherboard, did numerous software upgrades and downgrades and that it must be working now! with no success. Twice already I've booked in the phone twice on the same day because the problem re-occurred before I could get to my vehicle. I have been ignored the last 6 times I requested speedy feedback and not even a call back. SHOCKING SAMSUNG after being a customer for yrs.