The phrase "mixed them up" is correct and can be used in written English.
It is often used to describe a situation in which a number of things are confused or jumbled together. For example, "I was reorganizing the books on my shelf and ended up mixing them up."
"We played very, very well and mixed them up in the second half," said the Villanova coach, Rollie Massimino.
"One year we took everything from the 1990s, especially lettuce, and just mixed them up and put them under the pea trellising and got beautiful seed up". I've got the message: Fridge good, shed bad.
"Where you had the video security intercom, she had taken a sledge hammer to the wall to pull out the audio, video and electric cables, cut them and then mixed them up so they couldn't be used".
This year she appealed to the RAs to send small works – they took it in good spirit, she says – and mixed them up with hundreds more chosen from the 12,000 sent in by outsiders.
When we mixed them up, sometimes even the advertisers didn't notice.
He then mixed them up with a few photos used in iconic series: Marilyn Monroe as Andy Warhol's subject and Mt. Fuji as Hokosai's subject.
Tchatzu was a White Russian, had learned smatterings of three languages, and mixed them all up, and couldn't take telephone messages.
When I ran out of scratch (forget finding an Agway in Manhattan) I bought every organic grain in the health food store and mixed them all up — oats, wheat, barley, quinoa, sunflower seeds, millet.
Noting that her mother quotes directly from Sandra's journals in her book, which Sandra allowed her to use, she wrote, "my poor mother has taken some of my stories and writings and mixed them all up and put them out of context and sadly created a fantasy of me that she wants others and herself to believe.
They cut our hair and took our clothes and mixed them all up in big bureaus, so kids right away started fighting over clothes as they hurried to get dressed in the morning.
The Last of Us shifted narrative shooters to a new level; the role-playing shooter Borderlands mixed blast-'em-up idiocy with character progression in a more daring and anarchic way.
