Data Usage Meter woes

Like many others, I've become suspect of my reported data usage amounts from Cox.

In reading other posts, it becomes clear that Cox's fallback position is:   "We give you a Data Usage Meter.  Use it!"

Okay, that's fair enough and I'm trying to monitor my usage daily with this tool.   However, as often as not, it seems the data usage meter is not available due to maintenance.   When I try to view the meter, I get the message "Your Data Usage Meter is undergoing maintenance. Please try again in 24 hours."  (That is true again this morning about 08:00 EDST, Tuesday June 10th.)

When I go back the next day, sometimes I will see one day "blank", implying zero usage, while the following day's usage will be roughly doubled from the norm.    Other times, both days seem to be only guesstimates.

My biggest question is, can Cox's data usage meter be considered reliable at all?   Will it be fixed so that it's not constantly undergoing maintenance?

I'm a bit ignorant right now on third party measuring tools available to me, but I'm willing to learn.  I assume I can download another tool to measure with, and then compare with whatever Cox comes up with.   Is there one particular tool that's recommended?

Thank you!  :)