Both are considered warm growers so keeping their roots on the warm side and the media slightly damp not wet, going longer between waterings would be my advise.
They don't like cold feet just like us humans.
I'm sure there will the others coming along with more tips for you!
try to keep the leaves of bellina dry in winter, the close spacing of the leaves slows down drying if they get wet. that can be a problem if it gets cold at night.
This is what Peter Lin told me when I killed a lovely bellina 'TH' from him:
"I’m sorry to hear that. Because you are in the cooler area, it’s best to keep Phal bellina drier when it is cold. Don’t water the pot completely, but instead just mist the top layer moss frequently. This prevents roots from staying too wet for too long.
Phal bellina came from Indonesia where their night temperature doesn’t go below 70F year round."
Along the lines of what people have said above I would ask the question of 'how are you growing it'?
I have found that warm growing Phals don't like S/H in the winter if your conditions are cool. Here in the UK I don't ever let the house go cold but it does get cooler in the winter and my Phals just didn't like S/H in the winter (they loved it in the summer) and I lost a couple that way before I realised the problem (I saved others using a heat mat below them), I now don't use S/H on Phals.
I think the problem is that the clay pellets for S/H cool through evaporation which just drops the temps around the roots a couple of degrees. For warm loving plants in the winter that can be just a bit too much.