CTM installations - over quoted by R18,000

CTM installations came to measure for tiling and bathroom renovations. When I looked at the quote the measurements were significantly higher than what I measured. e.g. tiling: 140sqm I measured, they measured 210sqm. Skirtings: I measured +-100m, they measured 280m. I did the calculations and the difference amounted to R18,412 difference!!!! That is ridiculous. It amounts to *****. I have also commented on Twitter and intend going to their head office. I can't believe they are so *********.