Okay I've got the answer.
I asked Rain now and they said nope no app. I asked if they will consider developing one and they said "if we have an app in future, we will notify customers".

Obviously they will notify customers
if they have an app in the future, but what I want is for them to start working on the app now. They "will let management know".
The problem in my eyes is the scalability of the usage chart on the website's dashboard. It does not scale down to the MB level if you are not a big user. Many people like myself, use Rain as a backup when primary service fails, so we do not use much data. With Afrihost and Telkom as well, the chart scales down to MB level and up to GB level as your usage drops and rises. That would be nice if Rain could do that, better if in an app.