You could get one here. The problem is that the Ulephone does not support any network frequencies in the US or Canada so you won't be able to put a sim in it.
https://support.sonymobile.com/global-en/contactUs/
It may be something with an update that broke something, if I was you I would contact Sony directly.
There may not be any apps open, but things like email and social media can run in the background to be preloaded when you open it. This uses a lot of ram which could be contributing to your problem.