It's a Debenhams bra. Gorgeous range? Band fits fine in isolation but the minute I turn it round have back fat and scooping doesn't seem to put it all in. It's like muffin top in jeans at the back. I am a size 14 and not toned.
First up - Debenhams gorgeous are notoriously small
Now, when you say it doesn't pull in when you scoop - are the cups already full? If so, you need a bigger cup rather than band - if there isn't enough space in the cup then scooping doesn't work as it all just slides back out!
OK, that's the problem. If you fall out after scooping, you need more cup space. The measurement is only ever a starting point. Try an E, and possible even an F. Scoop like crazy before you decide if it fits - many of my bras look a bit empty until I've scooped.
This is probably what's causing the back fat to be so bad - the cups don't have enough room.