Only the honor of a paladin is unbreakable.

[Mewtarthio]

Symbol of Insanity causes insanity which causes confusion.
The spell confusion is a enchantment (compulsion) effect.

The spell protection from evil says:


So close. But no, it has to be an ability which lets them control you, causing insanity is still perfectly fine. Would give em a +2 on their many saves vs the symbol though.

Well, of course. I mean, it's a first-level abjuration, not a mind blank.