Charges for interest caused by SA Homeloans ignorent

I have sent the forms on 25 April 2016 to change the debit date to start end May but because of SA Home loan ignorance they did nothing which end up causing arrears on my side. They only change the debit date when i made inquiry yesterday, that's when they check the email i sent on 25 April. We asked them to be responsible for the arrears as it is their mistake to not check the email we sent but they couldn't help. The head office service is very bad.