This may or may not have any relevance in this case, but
Palio had this problem in an Uno. We discovered that the Earth had somehow broken. I rewired it and now both washers are working. As its both washers I would look for something electrical and as you say the fuse is OK its got to be the wiring or the switch (unlikely for both switches to fail at the same time). The earth is common to both pumps so if you can rig an earth to the body of the car from the black wires that go to the pumps (there were four on the Uno so you only need access to one of those) you can at least test it.
