I have a Samsung Galaxy S9 running Android 8.0.0 / G960FXXS2BRK3
It was acquired through an O2 contract but I've since moved to Sky.
I did allow it to upgrade once to Android 9 but this broke call recording, which is very useful to me, so I rolled it back. It was a PITA!
Now A10 is available for this phone but I'm just being offered A9 by the software.
My question is whether I must first upgrade to A9 then afterwards I'll be offered A10? The USB port is broken so there is no going back should I end up stranded on A9.
Software version the OS is offering me: G960FXXU2CSC8 / G960FOTF2CSC6 / G960FXXU2CSC1
OTA updates have to be done sequentially so yes, you need to be on 9 before you can get 10.
I'm not guaranteeing you will get 10 though as you have previously flashed firmware, you may have broken the update cycle.
I'd get the usb port fixed (the part costs £8) so you can flash 10 yourself.
Edit for spelling
You could try a call recording app @mark45623 ?
Track usage, upgrade and get support with the My O2 appDownload My O2