Billing

Last month i called Cell C call center to report my ****** phone so they can block it. To my surprise when i checked my account few days later there was usage of r6500. Mind you i have been on a contract with Cell C for almost 3 yrs & had NEVER , ever even went over R500 on my account. When i called call center to query that i was told that i never asked for the sim card to be blocked - which to me never made sense because if you reporting your phone ****** , surely your sim card would be in it. And as per the agent i spoke to I was never advised to block the sim card either & they saw it was an open ended contract. My other question was , i have been with cell c so long & never used that much on my account why am i then responsible for paying for someone's usage after reporting my phone ******, why cell c wait till its almost R7000 to block the acc , surely they could see my average spend on the contract. And when i queried if the phone is blocked how come the ***** still manage to use the sim, was told it could be on another device which they refuse to give me the IMEI of it so i can block - since they want me to pay the R7000 that was used on that phone