I did try resetting the wireless Carplay but it didn't help, and I didn't try the wired option as I want to use the wireless function. I do have a 22 car so it could be to do with the newer hardware but I can't be sure. When I was looking into the problem I found that users from all the VAG group were having similar problems, not just VW, funnily enough, BMW users have had no issue at all. Also, Spotify doesn't suffer the same issues with Carplay as Apple Music. Absolutely bizarre!
Do the messages from the data plan not stop if you close your account with Cubic via their website? I guess I'll see when it runs out.
Hopefully, we will see an update from either VW or Apple, or both in the future.
If anyone else had a similar problem and found a way to fix it without disabling the E-Sim or buying into the data plan please post it here, stop me going insane on my long commutes.