Data usage frustration

So we have recently checked the kids phones and laptops to confirm those very things.  And we have recently reset the router password and the wifi SSID password twice.   Here is the thing that concerns me.   We have EXACTLY the same devices and number of devices we had for the last several years with AT&T.  We never in all of those years went over the same 1TB of allowed monthly data with ATT.  NEVER in all those years.  No different devices.  Same Amazon Fire tv streaming,  same phones,  same laptops, etc.  NO NEW DEVICES or NO ADDITIONAL devices have been added.  We switched from ATT to Cox back in August because AT&T's problems with dropped service so often.  The first two weeks of COX were fine,  then all of a sudden the data usage exploded.  We questioned it,  a tech came out and looked at our setup and data went back down again to reasonable amounts.  NO CHANGE in DEVICES or ways they were being used.  Then all of a sudden day 2 of the new billing cycle the usage exploded again. Once again NO CHANGE in devices or how they were being used.    We had 112 gb of data used yesterday and we were out of town all day until Sunday evening.   When I look at my router I don't see any unknown devices showing up.   I do see that when I look at channels my wifi for the 2.4 service shows up listed twice.  Example a channel will show three devices on that channel and it may have another SSID that isn't mine (example an ATT SSID) and then it will list my wifi SSID as the other two.  I have changed the wifi channels and it does the same.  I can change my wifi to a channel with no other SSID's on it and it will show two SSID's once I am switched to that channel but will only list my SSID...

KittyPurry what is the model of your Netgear router? This will allow me to check to see if you can enable network monitoring on your router to see what device is consuming all the bandwidth. I don't know how old your kids are but at this point but one thing you might want to consider if that one of them could possibly be torrenting. Which means leaving on a computer or laptop with a torrent program running downloading and/or uploading movies, music etc.

Also I'm confused about your whole explanation of your SSID listed twice. You might want to do a google search reference WiFi spoofing. Which is essentially someone close (neighbor) using the exact same SSID name, same channel, with an amplified wireless signal. When you login to the spoofed SSID that person who set it up will record the password you enter to login. They will then know your WiFi password and will login to your network. They can also easily spoof a MAC address. Anyways to help nail this down I need your Netgear router model number.

Did you disconnect the cable modem for the entire day/night (24 hours)? I'm assuming this is what you did. But if you just disconnected the modem and plugged it back in immediately then that's not going to do anything helpful related to data usage. So if you did unplug your modem for 24 hours, you shouldn't have any data usage at all for that 24 hour period. If you did then there is something seriously wrong.