Struggling to change my debit order date

I recently resigned from my current employer and am currently serving my notice. As it is procedure in most companies, they pay you at the end of the month when serving your notice. I wanted to notify Capitec to amend the debit order for my loan account to the end of the month just for October as there will be no money in my account on the 20th (when the debit order usually goes off). I was told by the call centre that I need to physically go into the branch. when I went to Fourways Mall yesterday I was told that changing the date will not be possible and I need a letter from HR to say that I have changed the jobs. But this will present a problem for Capitec as if they say that I have resigned, Capitec cannot effect the change for some reason. I cannot understand why this is a case as I have been able to change all my debit order dates with no hassle. I was even willing to give them my new employer's details but they said this won't help my situation. please urgently assist with this as I do not want a debit order to bring unnecessary charges on my bank account. the fees they charge for debit orders are too high and I don't want this to affect me adversely