Have done so. Their response is it's caused by physical damage . That's why I thought I would ask here - knowing there would be good info!

You could try this? 

However, ultimately, you will probably need to stand your ground, insist it's a CGA issue due to goods failing to meet their intended purposes, and strongly insist your phone is repaired/replaced.  It's up to the business you purchased off (in NZ) to do this.

There is plenty of evidence on the internet to suggest this is a fault known to the manufacturer, and therefore Samsung should be repairing it.

Thanks. Yes, discovering plenty of similar complaints. Waiting for a new response from the NZ company I purchased from.

I have an S7 and I dropped it. Since then, I have had exactly the same line in exactly the same place on the screen (see below). A work colleague also has the same line in exactly the same place - also after dropping hers.

The issue you have is that the pink line obviously appears on a LOT of S7's after they are dropped, so proving that you have not dropped yours  sounds like it will be an uphill battle.

Here's mine:

The onus is on the company to provide proof you dropped it - if they can provide the irrefutable proof (I mean how did they come to their conclusion??) then so be it, however if not then you have a gaping hole to argue with them.