Oleander branches blackening - frost?
Hi everyone, I am new to this forum. I live in Calgary, Alberta and have an indoor potted Oleander. We purchased it last spring, and I had some trouble with it in the fall. I ended up spraying it down because I did some reading and found out it had spider mites (there was webbing everywhere). The leaves died off, but some were left alive. Then I pruned it in September/October, and all the leaves fell off by November. I've been watering it here and there at the bottom, but the cactus-mix soil is quite dry at the moment. Our house is not very humid at all, and it gets up to about 40% if we turn on the humidifier.
My concern is that the branches have started turning black/brown at the tips, and the browning is working its way down the length of the branches. It is getting about 3-4 hours of sunlight currently, and it is by the window along with the rest of my plants.
Am I underwatering this plant, or could this be frostbite? If anyone could give me tips that would be great. I also read another post on here about Oleanders, however I could not find the answer to my question.