Displayed usage disparity

Hello, I'm sorry if this ends up being a stupid question, but I recently called in about slow speeds and was told there was a warning of overuse on my account. The representative told me that there was a way to track data usage on my account and I compared this tool with a similar one on my router. My question is that on my router, which is an ASUS RT-AC68U, it says that I've used a combined transmission and reception total of 88.17 GB, but the usage tracker on my cox account displays a drastic 376.77 GB. Why is the router number so low? Thanks in advance!