Connection stopped

I bought this modem a week ago and put a Sim card into it. I connected it to my PC with an ethernet cable and all worked well. However, this morning all was working until the modem signal suddenly stopped. I got a sold orange light and four green bars. I checked that my sim card was active and on auto top up, indeed I added a bit to make sure I had data. It seems as though the modem is locking me out. When I turned it off and back on, I got a Netgear page on my PC. I duly signed in, and it just said I was not connected. I clicked connect and nothing happened. There is a box on the page that asks about limit and when billing starts, but not sure what this is. Please excuse my basic knowledge with this but a lot of the information I find goes over my head. Is the problem with the Sim supplier or the modem. Help please!