The My Account app says that it is not installed. And yet the icon is on my phone. I can see it says it's installed on Google play store. I even tried to Uninstall and then it just says to update it. No option to reinstall. My phone is a Galaxy A715w. I am able to run the app from the Google play store after updating it.
That's a bit odd.
Have you tried clearing cookies and cache of the app to see if that helps?
If the app is pre-installed in the phone, can you please try to disable it as well and then re-enable it?