Good to know you were refunded. Support really shouldn't have been that fussy over it. The exp was probably applied properly, and then capped afterwards. Which is probably the intended result. But you are correct, the stars you used were wasted, and should have been refunded right away without any hassle.
Guess I am a week late, but... Doesn't look like a glitch to me. The exp required to level from 62 to 63 is 119,281,359. 20% of that is 23,856,271.8 exp. The amount of experience you earned. I don't recall where I learned it, but I thought exp gained from killing a mob was capped at 20% since the beginning.