The usual:
1) Use the Report Lower Price links on your book page to report the free price for every venue it's free at. Repeat weekly.
2) Get your book on Google Play and then report it as above.
3) Consider using the "Make it Free" thread on kboards to get others to help you with #1.
4) Request directly from customer service if the above fails for several weeks.
Even given all that, some books never get price matched to free. It's a total crapshoot.
That bit I've highlighted is an important point. Price matching is not a one time thing. The book might revert to not free apparently randomly any time.
I've got a couple of free ones on Amazon and I've had to report a lower price for them about three or four times since I put them up a few months ago to get them to go free again, even though the free price never changed at Smashwords and the places it sends the books. There could have been other incidences I'm not aware of, say ones that happened after I got past the stage of checking them every day.
So now I check them once a week. You may want to check them every day with this push you're having. And possibly recruit some friends to also keep an eye on them and report lower price if needed.