[Q] Where in London can I repair this phone? topic

So I recently moved to the UK like a couple of months back and my T999 died, i.e. it was sporadically turning off by itself for a couple of days and then just DIED, it will not turn on, and no matter how many repair shops I wander into, nobody can fix it because it's an American phone.

Makes no sense to me because I was under the impression that all the S3s were made the same way but I guess not because it's not even registering on whatever system the Samsung centres use.

So my question is, does anyone know where in London I can go to fix an American Galaxy S3?