I have built a track in 4/4 but it was meant to be 12/8 so found an appropriate style in 12/8, updated, played etc but when I print it it still shows as 4/4.... why?

Because the Band-in-a-Box Program only understands 4/4. As far as Band-in-a-Box is concerned, each bar has four beats.

If a song is 3/4 times then Band-in-a-Box skips the fourth beat.

For 12/8 time Band-in-a-Box counts four beats to a bar with each beat counted in triplets.