Couple of questions,
Update: 2021 Mar I used neem oil, diluted and sprayed it every week for 3~4 months, and mixed a little muttermilk while watering, the sourwater helped these bugs stay away and no issues of these bugs this winter (2021), oh and also moved it completely outdoors and bigger pot. See them here
On the assumption that all the images are of the same plant, the problem is a rather heavy scale infestation - the fluffy white deposits are connected to the scale insect. If you are using this plant for edible purposes, you're restricted as to what measures you can take - there are some suggestions for control in this link https://homeguides.sfgate.com/rid-scale-curry-plant-35319.html, but if you have any rubbing alcohol or methylated spirits, take a cotton bud and dip it in, then just touch the brown scales which are present underneath the leaves and see if that makes it easier to get them off. Try not to get the methylated spirit on the leaves themselves.
The brown stuff on the underside of the leaf is “scale insect”. Unfortunately, curry leaves are prone to this. You can gently remove them with soap and water and then treat them with SB Plant invigorator every 10 days.
