Obviously, a DM should consider things very carefully before allowing "monster races", especially if they have potent spell-like abilities they can use at will. I'd consider making these abilities work 3/day and reducing the ECL a level or two to compensate. The books say "at will", but how many of them actually get to use them more than 3/day or so against PC's?
I think the rest of the party must have all had poor Will saves, because any 14th level spellcaster I can think of should be able to make that DC 17 save against that Suggestion spell without rolling (+9 class, +2 to +4 for Wisdom, +5 for that Cloak of Resistance everyone should have by 14th level). Or failed their save "for story purposes", which is letting the 'thid off easy.
Yeah, Hill Giants are easy. They are also CR 7, which should be earning your 14th level party minimal experience. Sooner or later, your 'thid will find an Iron Golem, and Plane Shift will be the only way out.
Plane Shift out of your problems, you say? You gotta specify a plane, you land several dozen miles off-target (read the spell), and most other planes are quite dangerous! Sure, you could Shift again if you find trouble, but the DM should be making you roll initiative to see if the monster gets a couple licks in first. You cannot Shift to exact locations, so you'll never quite get back to where you were. It is an excellent escape ability, but far from foolproof!