I have been overbilled on my data bundle account

Since May 2015 I have been querying the bill for my contract data bundle (which I have migrated it to prepaid) which was charged in the month of March and April 2015 which was very steep. I have requested an itemised billing so that I can get a clarity on what calls that I have made which could make the account to be huge.<br> I even complained twice here on Hellopeter because I was not getting assistance from the customer care call centre and emails.<br> The response that I got here were unsatisfactory and never fulfilled. I would like to get a refund for the amount that I have been overcharged.