Somebody hacking our Internet connection?

[Edan]

Bit of a dilemma, we recently got Internet but sometimes it cuts out for up to 24 hours then comes back sporadically. The problem is it says we have Internet, the modem is fine but we do not have a connection to the Internet. We think someone's has hacked our modem or something because every time we turn on the modem, a new connection comes up called belken 2g, then when we turn it off, that specific wifi disappears. To further this, our provider who happens to be my father says while our Internet was not working, someone downloaded 160gb on the network. Could someone be hacking our wifi to boost theirs?