Refusal by Capitec to change banking details for debit order

Today 5/09/2018 I called Capitec bank customer care to update my banking details for debit order deduction for the loan I have with them. The consultants told me that I must wait until the salary is paid into the new account number, send them bank statement and then they will update. I tried to explain to her that I have closed my previous FNB account that they were using and now I have updated my salary payment details with Nedbank account number. Still they told me that those are their rules. I simply do not understand why would a bank refuse a customer to update banking details so that the bank (Capitec) can get their money on time and the customer (myself) does not fall into the trap of a bad credit record by a missed payment. It is also an inconvenience that doesn't make sense. For that matter when I changed to FNB for the banking it was done over the phone and everything was fine but now its like the bank wants me to default on my payment when I am trying to maintain a good record with them.