hi Milly, welcome to the forum. \o/
Sorry to hear that you've had to post about a less than happy experience.
I don't understand how this mishap can have occurred when the items have all been assayed and hallmarked. This brings into question the issue of hallmarking itself does it not?
As to the letters of recall, top marks to GTV for owning up. However, given the total amounts involved are probably not huge in the scheme of GTV's annual turnover, I rather think that refunds would have been more appropriate and would have ultimately generated more goodwill rather than leaving customers with a quandary and lousy taste in their mouths.