They must have been already in the system. Did you cancel them very close to the due date?
This is from the Halifax online banking site, which also allows you to cancel online:
''How do I cancel a Direct Debit?
You can cancel a Direct Debit by contacting the bank or organisation to which the Direct Debit is paid. You can also cancel the Direct Debit online. To cancel a Direct Debit click on the Direct Debit you wish to cancel. Enter the date you want the Direct Debit to end on. Click ‘Continue’ to cancel the Direct Debit. Please note that you must give us at least 5 business days notice if you want to cancel a Direct Debit, and you must also contact the originator of the Direct Debit (the organisation to whom the Direct Debit is being paid) to inform them that they will no longer be allowed withdraw funds from your account and ensure that the cancellation is complete.''
I presume UB have something similar in their FAQ or T&C's - so if this applies I doubt if they would entertain you, but you could try. I still think it's strange that they were actually debited from your account, as the default cancellation date is usually the date that you actually cancel it online, although when you cancel one on the Halifax site the payee/originator details disappear completely from the direct debit section, not allowing you to see when you cancelled it.
I would ring on Monday & ask why they paid them after you had cancelled the authorisation.