Well, our recent experience is to be patient..... I was getting so frustrated at apparent lack of resolution that I did lots of googling and eventually found a report about how it can take several weeks for the chemical treatment to make its way through the fleece, and that users should be warned of this so that we don't worry and start trying to treat for something else...
Also, my suspicion is that at this time of year, with longer fleece it's really quite hard to eradicate the problem. We treated in early November, I think, and again at Christmas, and to be honest I think we will again next month, since I'm still seeing pulled wool....
I'm also reading that since less 'dipping' takes place now (which does 'eradicate'), lice is a more common / frequent problem.....
I'd be interested to hear how you get on ....