EE uses the standard Wi-Fi calling protocol that's built right into Android from, I think, Android 9 Pie. If your phone doesn't support it then I'm afraid you're most likely out of luck. Android 8 Oreo is 5 years old now and things have moved on a lot since then.
As for an update, if one was available then your phone would have downloaded and installed it or at least prompted you to do so by now. Note that until recently, Sony didn't have a clue what a firmware update was, so you were stuck on whatever Android version your phone shipped with.
