I don't have Xbox Live, I usually play online on PC, so I don't ever get emails or messages or anything like that. However, I have had my fair share of abuse from people who were sore losers, though it's nowhere near as prevalent on PC online as it is on console online. Surprisingly, the very sizeable community that still plays the original Halo on PC (and it's modding community) are very well behaved online, with only a very tiny number of idiots spoiling it for people. I had the misfortune to run into such an idiot during a game of CTF on the map Ice Fields on the original Halo. He was smack talking all through the match, and I managed to kill him once when he was in a Ghost and I was in the turret of a Warthog being driven by a teammate. It was a rocket turret, but the Warthog turrets can be hard to aim sometimes, and I was having to constantly shift my aim because my teammate was driving really erratically. My opponent, the little smack talking idiot (sounded like a kid, too), was quite a distance away, also driving really erratically, shooting at us. I managed to aim it perfectly for a split second, fired, and hit the guy square in the chest with a rocket. As soon as the guy respawned he started spamming me with text chat messages saying I was a 'n00b' and that he was going to find me and kill me, and that it doesn't take any skill at all to use a rocket launcher (never mind the circumstances we were in when I fired). I proceeded to track the guy down and kill him about five more times, to the amusement of the other people (on his team as well as mine), before he ragequit. Huh, I guess I must have no skill at Halo then, eh?
Regarding the OP, you aren't a cheat. You used legitimate gameplay to beat your opponent and he/she is just a sore loser, nothing more. Put it out of mind and take comfort in the fact that you are a better gamer, a more mature person, and a better sportsman, than your opponent is.