Overusage warning - what to do

I am on the essential package with Cox, (Up to 5 Mbps download speed
• Up to 1 Mbps upload speed ) with 100 GB monthly allowance, cost $42 (slow creep from original $30). Next step up is the Preferred package (• Up to 25 Mbps download speed • Up to 5 Mbps upload speed) Cost is $56, allowance 250GB)

For the first time I got warning about reaching the 100MB limit already half through this billing cycle. Looking on the consumption graph, last cycle there were mostly days of 3 GB per day use and one 10GB day, now there are mostly the +- 10GB days.

In my understanding, one Netflix film is 3-4 GB so additional 2 films per day would push me up. Need to speak with kids..
But I was traveling over the last week and had several facetime chats 10-15 min duration. How are those intensive on bandwith ? If ATT is allowing them on their iphones it can't be sooo much ?

I will possibly upgrade as the facetime calls at times suffered from dropouts, but is there a software for the airport which would anble me to monitor which internal IP address is consuming most ?