Over charge by R28k in one month - agents stopped answering calls

We are a small start up business (4 months old) and we have taken a 50G business LTE at R699 per month. This month (3rd August) with no notification or reason our line is cut. I contact the agent and he informs me that he will investigate. The next day i receive an invoice stating that I owe R28k and until this is paid the line will remain cut. I contact the agent and he agrees there is obviously an issue and will get it rectified immediately. I find out that it takes 48hrs for the line to get reactivated and in the mean time he supplies me with a router with 10G loaded until our line is activated. 48hrs stretched out to a week and finally the 10G runs out. During this time i have tried to call the agent and he does not answer his phone. I have received the agents supervisors name and number and try and contact him. No answer.I send multiple emails and get no response. I finally manage to contact the agent again (Last Friday) and am informed that that the credit has been reversed and just waiting on supervisor approval. All the while I am forced to use the data on my phone which is not cheap. when I call back on Monday the agent does not answer his phone. This goes on for two days with no response to any emails, phone calls and or SMS. We try his supervisor yesterday and he finally answers. I explain the situation to him and he agrees that there is obviously an issue. He promises me that he will call back and i sent through a copy of all the emails sent to him for his information. No phone call back. No response to emails. No answering his calls. I contact Cell C direct and get a breakdown of the charges. it seems that for what ever reason we had gone over the limit by 27G. If this is true my questions are: Why did the router not shut down when the Data cap had been reached? Why were we not informed either by email, sms or phone call? Why does it cost R1000 per gig when my contract has 50G for R699? Why does Cell C stop answering emails and phone calls? Where is the customer service from Cell C? As a small start up company is it Cell C's policy to try and destroy our company either by lack of internet or financially? I have copies of all emails send from the beginning of this fiasco along with records of all sms and phone logs.