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...