Data usage

ON 9 APRIL MY MODEM SIMCARD DON'T WANT TO CONNECT TO INTERNET, ON 13 APRIL 2016 TOOK IT TO TZANEEN VODASHOP IT WAS TESTED AND FOUND FAULTY. I PHONE 082 1958 AND CANCELLED THE CONTRACT AS IT EXPIRE 9 MAY 2016. ON 15 APRIL I RECEIVED A VODACOM SMS READING THEY HAVE DETECTED A HIGH DATA USAGE ON MY DATA SIMCARD *** OF R11933.71 IT'S IMPOSSIBLE THAT I COULD HAVE USED IT, MY VODACOM ACOUNT NO. QC189781