i don't understand

My Mr price account have been handed over to Blake associate. 08/07/15 i received a call from them telling me i owe R2000 from my Mr price account . when i went online om my Mr price account i only owe R1285. when i asked this lady that they are wrong they telling me it interest. it Interest for what they saying they been sending me letters and calling me that added up. i haven't receive any letter from Blake associate and they only called me to active a debit order i asked them to do it. why i am being harassed like this buy rude consultant because i was unemployed and i did mention i was no longer working to Mr price.