DISGUSTING SERVICE FROM CELL C

Good day I have been trying to change my debit order date for the last 3 months. i call the call center and get told that the date for the end of the month has been updated but when the end of the month arrived no deduction takes place. my deduction was for the 15 of the month previously and it stays like this. i have called and asked for a manager 4 times but gets told the manager will call, but to no avail. i refuse to keep on calling them and when i ask for a reference number for my calls i as told there is no such thing. What do u advise i do as this is very frustrating. PLEASE HELP.