How do I save my daisies?

[Foresttheout]

Complete novice here, I posted a while ago about wanting to grow daffodils abroad and somebody suggested instead I go to a local gardening center and find some flowers I love more suited to my climate. I did just that and have developed a small obsession with African daisies.
I bought 4 plants and they're in 2 big pots, however they don't seem to have taken very well, they are still flowering repeatedly where I de-head but the leaves are turning yellow at the tips then dying and the flower holding stems seem to be struggling to stay upright and flopping over I have no idea what I have done.

Any suggestions? also should I remove the dying leaves or just leave them be?

Are these Osteospermums? Not all are very hardy, and may have suffered from cold nights. Keep an eye on them, hopefully they will recover.

Yes they are, although I can't find the exact name of this particular colour they are a very deep pink colour with a few lighter pink flowers. Shouldn't have suffered from cold nights, I wasn't clear in my OP i'm not in the UK so the coldest night is probably 12/13 degrees at an absolute minimum. Although we are switching over to rainy season so it has gone from 20+ at night down to this so perhaps the change has gotten to them

Over watering can turn leaves yellow.
Osteospermum Don’t like to sit in wet soil so might be worth checking.