BIS services on Blackberry - R3000 account monthly

I have been logging queries for 4 months in a row, without any success or even feedback. Since my contract expired and I went over to a month-month basis, by bill has been astronomical - and that for DATA services. No-one can explain to me HOW this is possible. I eventually cancelled my line on 10 July - STILL I received a R 2800 account for the 10 days i used it in July 2015. The call centre agents just place you on hold for 20 minutes - never even comes back. Accounts division says speak to data - data says speak to account????? For the past 3 months ONLY by bill amounted to R 12000 - and STILL no-one can explain to me how or why???