Need more info...what size tank? Are you treating in DT or in a QT? What did they give you? What fish? How many?
I've never dealt with flukes, but have heard that FW
dips, every other day for three times will often clear this up. Adding Methylene Blue to the FW
dips is supposed to help. If that does not work, following with Formalin dips (two days apart, three times total) should do the trick.
Apparently the DT should be left fallow for 10 weeks to allow the worms to die off due to no host.