Bad modem

I bought a wi-fi modem from a telkom shop. The HUAWEI LTE CPE B315. I have my sim for my tablet and put it in my wifi router. Load data and connect my tablet on the system. The next morning the data was gone, 5gig data used through the night, thought its my tablet so i load another 5gig, the next day that 5gig was gone also, so i load another 3 gig, that was saterday evening, on sunday morning my 3 gig was gone to. I phone telkom call centre and the lady pick up the useage on that simcard. The reason she give me is that the modem use the internet during the night, from midnight until 7 in the morning. What a load af ****. The modem cost me R1300 and the internet another R800 for nothing. Now i sit with a modem that i cant use and all my internet gone. And the lady at telkom call centre said thats how the modem work. The number is ***. If telkom can go and look at that.