2 missed calls from this number and need to know where this number is calling from.
A related number would seem to be 01273341633. If it really is related to American Express then they are too push by far to waste time with, and by any definition a nuisance caller - they simply don't deserve your time!
I recommend that you submit a complaint to the ICO as they are using/asking for personal information inappropriately, as well as being a dam nuisance! http://www.ico.gov.uk/complaints/marketing.aspx