they have many altcoins and many exchanges listed on their website and it seems to me that it is a very difficult task for them to inspect every exchange and every altcoin they list on their site. But once you reported this anomaly, they should not ask you for evidence, instead they should investigate on their own and take due action.

two weeks ago I saw an altcoin increase  300% and was in the Rank 77 place and only had 3 small exchanges that made trade of that altcoin. I was very surprised by this, but unfortunately cases like these are a lot and are very scattered