Change of banking details

I have a debit order with them and recently changed my banking details. They don't want to change my banking account for the debit order because the account isn't 3 months old yet. I don't understand why as the account is in my name and my salary gets deposited in there. This is so pathetic and if I cancel my debit order I will be charged extra fees. I'm so glad my contract ends this year. I'm done with them!