Dying calathea (I think it's a calathea!)

Hi all,
I've had a thriving house plant, that I believe is a calathea for @ 4 years. Its been successfully split twice before. However this time instead of splitting o thought I'd just repot in a larger container and it is literally dying before my eyes. I dont think i disturbed anything, literally put in a larger pot with good multi purpose compost. Any ideas what's happened? Pics attached
I know they can be sensitive to temperature change but it's been Happy in the same spot for at least 2 years. I'm so disappointed and really quite sad with no obvious reason!