You should contact him, although (stereotypically) the kind of person who is around threadneedle st with a business card might well deny all knowledge the next day. There's no reason you should be out of pocket for his cock up!
Not willing to try yourself? I've found phones to be surprisingly durable to amateur repairs, as long as you have a decent enough guide/video to work from and if something isn't going don't shove it.
No experience here but another place that hires out a stand and tools is Bikeworks, possibly worth considering if that's what you want to do. They have a big stock of random parts and bits and bobs in case you find you need an odd shaped nut or extra spacer to make it all work..
You should contact him, although (stereotypically) the kind of person who is around threadneedle st with a business card might well deny all knowledge the next day. There's no reason you should be out of pocket for his cock up!