lisa,
I'm not sure this will reach you before you leave Levanto, but I'll try anyway....
You should be able to buy your ticket for the Malpensa Express in Levanto. I wouldn't be too concerned about the other traveller you saw that was having trouble using the Kiosk, as there could be several explanations for his problem - he may have punched the wrong buttons, the machine may have been malfunctioning at the time or the network may have been down (I've seen that happen). The Kiosks work well, when they're working. In any case, there's always the ticket window.
You could also visit the full service station in Monterosso and deal with the ticket office there. I've found that the agents speak reasonably good English, but it's important to speak slowly and clearly. It sometimes helps to have the travel details written on a piece of paper that you can show them - train no's, desired departure times (listed in 24-hour time) and date (written in European date format).
If you need to buy the ticket at Milano Centrale, there are a couple of options. If you use the Kiosks at track level, you'll probably find that they're crowded at times (but there are lots of machines), and that's where you may be approached by "helpers". Be sure to watch your luggage while buying tickets! You could also go down two floors from track level on the "moving sidewalks" to the ticket office. As I recall, there are a number of Kiosks there, and they may not be as busy, and may not have as many "helpers" loitering about.
I'd suggest taking care of the tickets in Levanto or Monterosso if at all possible, as you DON'T want to be in the position of having to use the ticket office in Milano Centrale as there's usually a HUGE queue! You could leave for the station in Levanto about 15 minutes early, as that should be enough time to buy the ticket either at the office or from a Kiosk. DON'T FORGET to validate the ticket prior to boarding the Malpensa Express.
Enjoy the rest of your trip!