Cox Data Usage, Should I upgrade?

So just today, i received an email from Cox about my data usage exceeding the data plan.  The email states my data plan includes 300 GB, where for this month, my house has used 605 GB, more than doubling our data plan.  Lately, our internet has been having problems where the wifi would just crash and a simple restart would fix it.  An hour later, the same problem would reoccur and I'm not sure if it is because I am using an old modem or because my house is using too much data.  I am living with 8 other people, so 9 people total including myself.  6 out of the 9 people regularly game on either a desktop or laptop computer.  We're just college students and upgrading our bundle for better internet is just way too much for our budget since we have a tv and internet bundle deal: $139.99/mo.  The upgrade is $189.99/mo.  Please help.  I don't want Cox to terminate our service since the internet is so vital to our schoolwork and our future.