over billing

hi i have a cellphone contract with cell c it was done over the phone... the agreed amount was +/-R245 i had no problem with the amount, that was done in december of 2013... <br> in August 2014 i started realizing that my debit started increasing i cntacted cell c and was told it was due to internet usage, the next month the amount increased again and this time i requested all my statements to be sent as they claimed to have charged on non cell c numbers.<br> november i spoke to a team leader who requested that i send an email and someone would come back to me and still i have had no feedback i am currently owing R1800 if not more but the phone has been off since january 2015 i put the sim away.... no one is willing to answer i have also requested voice recordings but nothing has been done !!!