You err.
If is most certainly assur to own chometz on erev Pesach after chatzos mid’oraisa. Most Rishonim hold it’s an asei, but there is an opinion that bal yero’eh and bal yimotzeh also start then.
As numerous posters have commented, and I showed you sources, the accepted minhag is to not eat kitniyos from the same time we stop eating chometz.