Debit Order Nightmare

I have an account with Bradlows, wherein the payment of this account is made to Bradlows via a debit order instruction to Connect Financial Solutions, my request was that the debit order should run or rather debit my account on the 15th of every month as this is my pay date. Connect Financial Solution have now on two occasions where the 15th falls on a Monday they debit my order on the 13th being a Saturday, where at this time there are no funds to cater for this order which result in my bank account having charges that i must pay for or where there funds are available on my account but are not intended for this debit order according to our arrangement. I have tried to call this Connect Financial Services requesting to cancel the debit order and a consultant by the name of Nicole told me i cant cancel the debit order after i've clearly stated the reasons why. How possible is that i can get into a credit agreement with a financial institution and i request cancellation of a debit order and i am being told it isnt possible i would rather pay cash via EFT than having my account incurring unnecessary bank charges