If body proportions remained the same, volume and weight of a 12-foot humanoid would indeed appear and weigh three to four times the size of a regular six-foot human.
If anything, the above statement seems to validate having been made by someone with a first-hand observation.
As you increase all dimensions of a solid equally, the surface and cross-sectional areas increase as the square of the dimensional increase, and the volume increases as the cube. Thus a 12-foot-tall human’s weight would be 8 times that of a 6-foot human having the same proportions.