Set data limits per line

It's so upsetting that you call customer care to ask about having to set bandwidth limits on each line. I have 10 lines and I want to set a bandwidth limit on certain line (kids) and I was told I had to pay for smart limits (4.99 per line) so I when ahead and added the ferure but to my surprise AT&T employees don't know there own products because it still doesn't add data limits. All it does it has spending limits, text limits, & data turn off. Why would I pay 4.99 per line just to manually turn data off and watch for next month and turn it off when they reach my desire limit ( keep in mind I have to check every day to see how much they used and turn it off when they reach my desire limit) why does AT&T does this? Why is it all about making a quick buck on people. They don't have that because they want u to go over and pay hefty data charges. There got to be a way to prevent it, why when the government is up everyone business why haven't they made this a require feature to prevent cell phone companies from taking advantage of customers!