Hey let me help you with this.
You don't have any proper "Evidence" which means, you could be saying everything as a lie. Moreover you don't tell us the "Whole Story", like "What did you do the previous round" probably, or what did you say or anything that made him "Slay* you as you claim.
+ You can simply ask the admin first, WHY did you slay me? Instead of reporting him immediately, as I believe, our panels can't do much about it, as it was a slay which usually happens due a rule you did not follow. Now for next time, I suggest you to talk to the admin first, before taking this further action.