Debit order details change

I’ve been trying to change my debit order details on my onAir account from last year,Nov 2020 till now and every time I call I get told that my debit order details will be changed from my previous account to my current account but never does,I called numerous times and it’s so frustrating because the debit order never comes through to my new account,I called again in February 2021 only to learn that my account was in arrears of which I understood because there was never a debit order that went through so I gave them my new account again to debit in March but still no debit order went off from my new account this month when I got paid,so today I called again and I found out that my arrears have gone up again and I did the same thing of giving them my new account but I am so frustrated and fed up of calling over and over again to change banking details but I never get help,I don’t know what to do now ,I’m even thinking of canceling this account because I don’t want to ruin my credit profile because of such a petty thing,they fail to execute such a simple simple request from a client,I’m really frustrated