Terrible service

I've been struggling all morning to speak to someone who can assist. I upgraded a contract to 600gb data and apparently that's finished in 1 month. The router is still new and not everyone has even connected to it yet. With my previous network provider of 2 years we never got close to the 200gb allocated so it's impossible for 600gb to be finished so quick. And nobody can give me answers on the usage or next steps