First, Trump had just frozen military aid to Ukraine days prior to the call. He didn't have to say he did that, the Ukrainian President already knew.
Second, IG investigation report will be the next one released. That's the one where the IG interviewed the first hand witnesses and deemed the whistleblowers complaint to be credible and urgent.
Here is a handy timeline if you're interested in more breadth.
https://www.reuters.com/article/us-usa-trump-whistleblower-timeline/trump-and-ukraine-timeline-of-events-in-the-controversy-idUSKBN1WB25BEdited by limenats at 16:25:58 on 09/26/19