S5 mini - Why won't 4G work?

[AC Question]

Hi Community,

I have searched but can't find any info on my issue.

In short the 4G (LTE) won't function on my device. Below is what I know/have tried. Hoping someone has some ideas.

Samsung mini S5 SM-G800Y

- The device is correct band for 4G N/W I am on (band 4 1800MHz). It was sold originally by the N/W provider I am using (2degrees New Zealand) and confirmed good for their N/W. Also it came factory reset so I don't think has anything custom.. although can check if theres some way.
- I have tried a friends sim card (works on 4G on his S5) and doesn't get 4G on mine (i.e. not my sim)
- I have enabled the network correctly, and power cycled several times (i.e 4g/3g/2g auto is selected)
- I am on latest IOS (KitKat 4.4.2)

I feel like maybe my unit is faulty but would have thought if the phone wasn't working for 4G then I would see 3G issues (I don't).

Finally its not under warranty so there'l be no sending it off for someone else to solve (hence why I am here trying to solve).

Cheers for any help -greatly appreciated.