I did as you suggested and after an hour of chat, it emerged that there are radio buttons within the Sky Store account (which I had never accessed as an "old" Sky customer i.e. pre 2000). I suspect that internal Sky IT changes mean that, my simply telling Sky ID as invited that both my billing address and Sky Store address had changed following relocation ( and still showing after 2.5 years later), no one had told me to then log in to Sky Store and click the radio button next to my new address (listed in Sky Store) to change future deliveries from my old address to the new one. Brilliant work!
Anyway, I've clicked the little radio button now and will test (tomorrow after overnight processing) with another purchase. Thanks for your help @caesarome
