Unable to sort billing out since February 2015

My wife has 2 cell phone accounts through Telkom Mobile. Since February they have been putting the debit order through at different times in the month. We contracted for the debit order to go off on the last day of the month, which it was doing for years, then all of a sudden the debit order doesn't go off and we phone them to advise and they don't have an answer, then we pay it manually and a couple of days later the debit order comes through. Then we have to get the bank to return it, as it was not planned for and the bank charges you for it. At the end of May the debit order went off as it was supposed to at the end of the month, then at the end of June it never went off again. We phone them and they say they don't know why, but we must make a manual payment, which we did. Now on 14 July the debit order goes through again. Come on guys this is not on, we are contracted to have the debit order go through on the last day of the month, why does it keep changing? The incompetence is astonishing!! My wife's main cell number is ***, please can we get somebody competent to sort this out NOW and stop inconveniencing us.