Yes Cox Cable Internet does place a limit on the amount of data that you can use through their service.
The limit on Cox Cable Internet service is 1 TB of data and then after 1 TB of data you're charged additional money for the extra data you use in that month.
When you go over the 1 TB data limit with Cox Cable Internet you're charged an additional $10.00 per every 50 GB of data you use after that.
Most casual users of the Internet will never exceed the 1 TB data limit but if you're a heavy game user who plays games online a lot or downloads a lot of games, movies etc or watch a lot of videos then you could easily blow through the 1 TB of data.
Even Streaming Netflix and other movies can use a lot of data especially if more than one person is streaming movies and shows at one time.