Is my ISP telling me the truth, or is it a scam?

hello good people
I don't have a good knowledge of internet stuff, but I am repeatedly facing a problem with my internet connection, and when I call the ISP, he told me that I am using the internet too much and I need to decrease my use, or I should buy another router that could control my internet megabytes draining, but when i registered with this ISP he told me you can use unlimited megabytes with no problems there will be no restricted usages the speed that i have from is a 30 m/s monthly
But now he is telling me you have drained the whole 30m

I have unlimited 30m/s in the month, and I have used it all. How will that be possible?