I've only been playing for two years, since I was fourteen, and have never gotten a char past level 37. It's sad, I barely know anything about CF.
But, I know a fair bit about cheating.
The first time I did it was because I didn't think it would be a big deal. I didn't think the Imms would care. But I got ROTD'd and talked to. The Imm only made me drop the stuff I'd received. He didn't slay me or do anything. He transfered me back and I went on playing.
The next time I was treated more harshly. I tried to lie about what I did, so he slew me. I believe I tried a third time with the same result.
My point is that my experiences with the Imms have been extremely satisfying. I am GLAD that they slew me twice, and whipped me into shape. Also, they helped me a whole lot when I was learning the ropes. It is extremely unlikely that an Imm would slay you without pretty good evidence of cheating, although they might do it for being rude. From the helpfile on Immortals:
"Immortals are far beyond the abilities of mortals, and only the most foolish would even think to approach one with anything less than awe and reverence."
Since you're denied now, I would suggest emailing the Imms with a message saying that you won't do anything like this again, promise that you did not actually mean to cheat, apologize for rudeness (for good measure), and include your IP. Remember to keep it polite.