MR1100 Router Drawing Data on Its Own-Tech Person Called It "Memory Leak"??

Grandson visited & for abt 3 hrs used our MR1100 router to game on computer with a couple of friends also using a voice app. (They have regular fiber optics wifi at home.) When he left, I learned he did not "disconnect" the wifi connection on laptop, just turned off laptop & left.  For the next five days the router drew down 10 - 25 GB of our data per day.  Discovered this on day 4 when AT&T data warnings started arriving. On Day 5 had to change plan to 100GB so would have date for remainder of billing cycle since it had just began day before he arrived. Never watched data that close before because we never exceeded our 50 GB data plan. I finally unplugged the MR1100 & removed battery to make it go dead & reboot.  Cdn't find other way to reboot.  All AT&T would say is what I already knew which was the data details showing 10-25 GB in 900mb units for days; it was my hardware problem.  Finally I went by Best Buy to ask the tech guys how this could happen. One tech, prev T-Mobile employee, said it is known problem with some routers called "memory leak" where the router doesn't understand the party is over & that the laptop w game has left the house.  The router keeps trying to reach out and reconnect with laptop/game creating the data draws.  It stopped when I forced it to reboot.  Otherwise, he suggested a hard reset back to factory settings.  Has anyone else had this experience?  A few other instances of data draw when I am not home concerns us...is it router or AT&T sucking data?