If you follow @RobertZ instructions with navigating to data saver, then toggle that on and see what happens. I think that "restrict background data" you have in your battery settings is something the battery utilizes when conserving power and restricting background processes. If you want to restrict data itself, then try the data saver.
I believe that those are 2 independent services. "restrict background data" is used for conserving battery - this service is used to just limit data. With "data saver", its user initiated and is used app wide(all apps will be affected unless flagged as an exception by you).
Hope this helps,