You appear to have replaced the entire font with your new font.
A font is a series of designs (glyphs) associated with different character positions. So a W in Times New Roman looks different to an W in Comic Sans.
Dingbat/icon fonts put arbitrary images in place of letters.
Your new image should be where the S is. As it is not, and there is no character at that position in the font file, your browser will be defaulting to a different font (which, as might be expected, has an S allocated to the S position).
You will probably find that other icons around the site look wrong, because you've swapped out the whole .woff file.
You need to use a font editor that will let you set glyphs in the right place.