Insecure online portal technology

Last week I had a call from Absa ***** asking me if I’m aware of the online purchase transactions that happened on my account around few minutes ago, then I said no, then they advised me to go to a bank and get a new bank card so that I can get a new bank number, so I did that and also emailed the bank transactions to dispute@ absa then I had a reply of I must highlight the transactions then I did that then I received an auto reply saying the receipts mailbox is full. I then called the ***** dpt then I was told to email back then still I got the same auto reply. So it has been 10 days still no reply from absa. The worst is I did not authorize or buy online on Monday the 7th!!!! So their online security is insecure if things like this happens