debit order changes

I called cellc customer service on the 26 February 2016 to change my debit order details, the lady on the other side told me that I must call again in 2 or 3 days time, the reason was, because my current debit order did not activate yet. I called again on Monday 07 March 2016 and the agent, Babalo kindly changed my details for me, when confirming the activation date for my new debit order instructions, Babalo informed me that the new debit order will only activate at the end of April, when I asked him what about the end of March, he simply told me that I should have called them on the 1st of March. I went to the branch in Claremont Cape Town, where Lee-Anne confirmed what Babalo have said. When I asked why it is like this, she used the policy card on me. She also confirmed what I feared, they will still attempt to debit money from my old account, which I am planning to close. I dont know what else to do to make cellc activate my debit order so that my payment can go off in my new account at the end of March. I find it amazing that a big bussiness like cellc make only one day available for their customers to change their debit details. Pls help,