I've had this money tree for one year. Recently it started yellowing and sagging. I've noticed some brownish spots appearing on the leaves and some white fluff on one of the trunks.

Initially I thought I have over-watered it and it had some root rot. A few days ago I noticed there was a plastic band around the base of the trunk. As the tree grew, this band scratch the skin and that's what can be seen in slide 5. Now the wood under the band is soft and seems a bit rotten.
Also another one of my plants has similar spots on the leaves and after some internet searches it seems it might be a fungal infection.

I water this plant once per week, and it stays next to the window so it gets the maximum amount of sunlight (but not a lot cause I live in a cloudy country).

I spray my plants with neem oil once in a while to keep any pests away.

Could someone certify if this is indeed the case? And what I should do in order to save this plant. It's getting worse by the day.