1st. Don't rage so much. It won't help you anyway and it may start some unpleasant argument for you. Just state you position in calm way, possible demo explanation and wait for other opinions/decision. It is admin's job to ban people when they suspect a player in cheating.
2nd. I have seen roLL and sHaRaN playing together at the same time, so different people for sure.
3rd. There are a lot of people with steam who use cheats. So, 'I have steam - I don't cheat' doesn't count.
Last, my opinion about demo: 3rd kill on long while flashed is weird, but maybe just luck. 3rd round - clearly 16bits or low graphics. But I don't see any convincing wh movements.