How do I find out how may GB left on my wifi?

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(i hope i phrased the question correctly) So i got a message yesterday on the modem/router thing that said that i have nearly reached my credit limit and today i got another message saying that my bill is ready to view. Does this mean that my internet credits have reset for the month? we pay it pay monthly btw. I don't know how to check how many GB or MB i have left and i logged into the gateway thing on the laptop that lets you check the wifi settings and SMS's and stuff but i cant find any information anywhere on how much GB i have left. It tells how much data has been sent and received so maybe i could work it out from there? i dunno i need help cus i'm too scared to go on thee internet in case i go over the limit and have to pay extra
But does your credit limit reset after getting the bill?
But does your credit limit reset after getting the bill?