I have tried both freezing it and distillation... seems that unless you have a seed crystal, freezing it takes a LONG time, took literally weeks for crystals to form.
Distillation requires more effort, but can be done in a few hours. At ~12mmHg (-30 or so inches of Hg) I had safrole come over at ~110C. This is with a water aspirator (using icy cold water), btw, with a real vacuum source it would be better.
Check for leaks as suggested. I have a little flow meter (basically a little glass contraption with a propeller in it) that I put inline with the vacuum source to indicate whether or not the vacuum is removing anything - if it doesn't stop spinning continously I have a leak. Also check for vapours in your condensor... I once had a leak around the thermometer adapter, and noticed streaks of condensing vapour rushing down the condensor and out to the vacuum supply (the inrushing air was carrying the vapour down - lost material!).
Also test your essential oil for safrole. UTFSE, as I recall it turns purple in sulfuric acid, is denser than water... I think there are other tests.