Failure to change installment date

Logging requests to change Installment dates on their website falls on deaf ears. They have the functionality, but clearly not the ability to attend to these queries. Logged a requests online a month ago, again this month they tried to debit my account on the "wrong" day. Now I'm getting inundated with calls about the installment, which might I add, will be paid manually, yet again, on the day I have requested them to change the DO date to. Clearly they are not interested in this, and would rather continue to debit and put my credit score into disrepute! Utterly SHOCKING!