Unfair business practice Planet 42 -***

I have informed planet42 two months in advance that my banking details where my salary is paid have changed. They decided to ignore that and went on to deduct money from the old account in the process causing me unnecessary bank penalties. In of their emails dated 15 November 2024 they have admitted that it is their fault. However they still want me to pay the arrears which came as a result of their negligence. They don't even show remorse for their mistake or the so called oversight as they call it, for me this happened as a result of their gross negligence of which they are not prepared to take responsibility. Instead they continue harassing me with messages and emails that I should pay for arrears which resulted because of their gross negligence. I have a contractual obligation to notify Planet42 if there are changes in my life including but not limited to the changing bank details, they have an obligation to update their system, but they failed to do so. This unfair business practice and it cannot be allowed to continue.