Upgrade to what? I have the top tier internet plan from them and I have a 300gb limit as well.
Then you don't have the top tier plan. The limit for the top tier plan is 400Gb and in OKC costs $99/month for home (not business) users. That plan also provides a 100Mbs speed as opposed to the plan you're on which is limited to 50Mbs. (at least in OKC - Tulsa may be different)