Thank you so much for the time and effort you put into this answer. After a quick check, the Xbox and Microsoft accounts are linked. I have also contacted Microsoft directly and, after working through the list they provided (many of which I already tried) it turned out to be the reinstallation of Windows 11 setting my time/date region incorrectly. My PC showed the correct time and date so I thought it was ok, but looking a little deeper the correct (London) region had not been set. Anyway, I'm very happy to have my sim back, just have to wait for my awful connection speed to get all the updates. Thanks again, it really is appreciated. :) John.