Negligence from Vodacom

Hi My name is kabelo Thulo i seem to have a problem with vodacom i had a contract with them for some time kept on upgrading it for Data deals as i had paid up my phone. They have sent me a letter of demand saying I owe them R 975.53 I called asking where this is coming from and why was i not contacted if there was no payment made for months straight they did not or could not confirm why that happened and why i was handed over. I called the attorneys i was handed over to and they too do not know why i was handed over as they themselves dont have a reasonable explanation they only opted i pay... i do not appreciate such negligence why was i not contacted if there were no payments towards the contract agreement and whats even more annoying is that this arrangement (Payment arrangement ) was a debit order so this is really upsetting why was there no contact from vodacom