Why is Maps using outrageous amounts of background data? I just got three auto-top up notifications amounting to total of about $50 from my network carrier.

Upon checking data usage, I see that this month shot up to 5gb+ and the details show it was almost all due to Maps, (please refer to screenshot).
The breakdown says 2.13 MB of foreground data and 5.15GB of background!!!
The messages from my carrier were sent within a 35 minute window.
This is expensive and outrageous. What's causing it and how do I prevent this?!!

I'm using Blu Lifemark 4G. It's an american company who had had security issues relates to Chinese interference but they said the new software releases fixed that. My android version is 5.1. Maps version: 9.67.1
You can prevent it by activating "Restrict app background data" (seen in your second screenshot). 

There is also the Datally app (from Google itself), which allows you to block internet access for different apps.