9 months later - still no reply

Received a bill in June 2014 with R2000 of data usage that we can not trace to any activity on our side. Since then I have made 20 odd calls, send many-many emails & lodged tickets from the website - absolutely no response. Every time I speak to an agent, I get promised that action will now be taken. Soon after I receive an automated email stating that case xyz has been opened and a short while later \ case has been closed"with absolutely NO feedback"