I emailed a complaint in to Sky which was picked up by the Sky Streaming support team. They were able to fix the issue by removing Paramount+ Premium from my account 'in the backend'. I have Sky Cinema, so they also did something to re-associate my Paramount account with Sky so that I get Paramount+ Basic via Sky (which is included in Sky Cinema).
The option to switch to Paramount+ Premium via an app subscription on my Sky Stream is available again, although I haven't done this yet.
