Debit order goes off with arranged manual debit order

I phoned during the week to see if there was a payment arrangement that could be made. I was told the debit order would try for the full amount and if it rejected the a manual debit order for half the amount would go off. Now I see the full amount was debited together with the manual debit order. Now I cant pay other debit order because of this! this is ridiculous service! You have now caused other debit order to be rejected and incur costs that I can not afford! I cant believe this type of incompetence!