Hi Toby,
I was just fighting with a similar issue.
You may need to re-instal the sim from your XBox account. Nothing should be lost since you purchased the game. With all updates, the re-instaling can take up to 5 hours (have it in mind...). After that you may need to download again and install any add-ons. But all is stored in your MS account and the account recognises for what you paid. When I started the sim after the re-nstal, I even found my system settings re-stored, so nothing was lost
Good Luck,