Too bad that the soap didn't work, it seems to be quite a controversial subject
found this:
Discussion on soap and RLS I wonder if this means that breaking a mirror won't cause 7 years of bad luck, or that cats don't in fact steal the breath from babies after all?
But still, although this soap thing seems to be listed as one of those "old wives tales" (never understood that phrase) it is listed as "undetermined" in Snopes, and there are a few other ideas here to try:
Snopes on Leg Cramps
