The shop is mistaken - 12mm bolts are what is needed.
Go to the Ingall's engineering website and enter your vehicle details and see what part number it calls out for the cam bolts - the other way is to remove one of the existing strut-spindle bolts and measure the diameter - which I believe you've already done.
bentparts - the actual bolt part is smaller, but the "cam" part has to match the original bolt diameter, which is why it's possible to determine the cam bolt needed by measuring the original mounting bolt.
I discovered this after measuring the bolts on a number of vehicles - for example a Suzuki Swift takes the same Ingalls part number as the Suzuki Vitara - sounds strange doesn't it? I needed to get cam bolts for a Mitsubishi that's not listed in the Ingalls application guide, worked out that it needed 12mm, Ingalls wouldn't respond to email so I took the chance and ordered them, and have them installed for about a year now.