It sounds like the temperature extreme may have affected the aperture mechanism in your lens or the lens side of the communication path between the camera and the aperture mechanism.

It might be something as simple as a lubricant freezing and crystallising in a way that it no longer has the same properties after warming back up. It could be something as catastrophic as moisture inside the lens expanding as it froze and causing a continuity issue on a printed circuit board inside the lens.

In practical terms there's not much difference regardless of the cause: just having someone open the lens up to look at it is probably going to cost more than the lens is worth. You can try more passive 'repair' methods such as keeping the lens warm and dry for several days and see if that helps. Otherwise I'm afraid it is probably time to consider another lens or you can continue using the lens in away that works around the fault.

The original non-IS versions of the EF-S 18-55mm kit lenses were not that good. The IS versions are better, but they are still on the lower end of optical performance compared to most of the lenses available for your Canon EOS camera. The 80D is a very capable camera. You can take this opportunity to put a lens on it that will allow you and your camera to more fully reach your potential.