Again, unless you have domain expertise I suspect you are drastically underestimating the complexity of reality. As I alluded to earlier metering, pricing, and billing are _at least_ three separate complicated problems in substantial systems. There are multiple metering dimensions that interact with each other, time, and periodicity at a minimum. Saying “do billing better” without either a thorough understanding of the existing system, or an actual concrete proposal, is not useful.
Being separate systems is fine as long as they can all calculate a number within the time it takes to make a cup of coffee. That's not hard if you actually make it a design goal.
I'm sorry that "prioritize it" isn't very helpful, but it's true. If the calculation takes longer than that, it's a management-induced problem.
If we're positing a system that can already do that, then you need to be more specific about the problem you're describing because it's not obvious.
