You’ve taken all the steps you believe are necessary to rank a page for a particular keyword – and then another page on your site shows up for that keyword.
This is a frustrating yet common problem. When the “wrong” page is showing up, Google isn’t recognizing your intended page as the best destination for traffic, for some reason.
Despite the fact that your intended page might be the best destination, logic doesn’t apply here; only algorithms determine the ranking and various SEO techniques can attempt to correct it.