Over charge on data usage

For months I have received high bills from Vodacom its clear data usage is high. After contacting the call centre on many occasions & going to see the branch, the response is there are no issues. I added contract for a Wi-Fi device as advised I was in the wrong. All updates run on WI-FI only. I went to Vodaworld to see a consultant (extremely friendly, sarcasm) she could not assist and referred me to data centre. The data cons. was only available on telephone, I spoke to Mohammed, advised him of my issue, he agreed something was wrong after checking my phone settings with me. I do not agree with the billing & I'm sitting with a Neotel home and Voda Wifi, my data usage on my cell is low therefore the extra devices to cut costs (cause i am in the wrong). I cancelled my contract on 27/03/15 - paid in full and now on pre-paid. The laid back treatment received is unprofessional. Your consultant was more than willing to cancel my contract rather than to get someone in a higher position to assist me and resolve the problem. The last debit order that went off was reversed, this amount will only be made once I have received a full investigation on data usage for the last 6 months.