Data usage meter doesn't match router usage reports.

I have gone over my data usage cap the last 2 months. Previously my data usage was between 300-600 GB per month, well under the cap. I decided to keep track of the total input/output of data from my tp-link router. For the last 2 days the Cox usage meter says I used ~80GB, but my router says I have downloaded ~ 4GB. Does anyone sees have a discrepancy like this? Is there anything else that could giving a false report to Cox?