Simple: Beating the Seekers with magic at this point is practically impossible unless you want to burn a TON of mana. You get a few decent attack spells in Chapter 4. For now, I suggest using "Summon Skeleton" in addition to your own fighting, or "Iceblock" to freeze them, and then hit'em with your stick.

By the way, Magician is by far the hardest class to play. If you can do it as a Magician, the other classes should be pretty straight forward.