I ended up contacting them via facebook.
I purchased my phone in the US as an unlocked phone with the purpose of being able to use it in other countries. They have told me that the phone can only now be used in the US, essentially giving a 9 month old brick.
This was after being informed that there was an international patch available.
I am going to try to "flash" my phone and see if that works, but I daresay that my next phone will not be a Samsung.
Factory reseting does not work either.
Facebook contact is https://www.facebook.com/samsungsupport/
I also am now getting the dreaded 'IMS Service Keeps Stopping' message directly after installing the
latest updates this morning 7th Sep 2019 on my Galaxy S9 Plus.
I have tried all the suggestions mentioned including as a last resort doing a hardware factory reset.
The message came back immediately after restarting following the factory reset before even restoring anything - this suggests to me that there is a serious problem with the latest updates.
The phone is now essentially unusable in that it is very unresponsive and the battery goes flat in
about 3 or 4 hours!
Model phone: SM-G965U1
Harware revision: 1.1
Update version: G965U1UEU6CSH7
Size: 630.81 MB
Security patch level: 1-Aug-2019
Kinda makes me glad I still have a Galaxy S7 and it still works fine after the last update. But I don't use it internationally.
Maybe US Samsung phones get "locked" into US, despite a international-capability claim.
It appears that Samsung have rolled out an update which fixes this problem. I updated my phone 2 days ago, and all seems well so far - however, after this whole experience, I am waiting for a few more days before I say that I'm happy!!