Federal Return E-file

Return rejected as AGI on 2019 tax return was said not to match what what printed on my 2020 return.

Called and one of your reps said I needed to go to IRS web site and get a transcript of 2019 tax return.

Called again as thought  perhaps my account had been hacked and someone else was claiming my refund and was told the reason my federal return was rejected was because I needed to mail my return and not e-file. Which of your reps was correct and if I need to mail my return, why does that not come up when e-filing as a possible reason, especially since TurboTax needs to update every time I turn it on?