If a Direct Debit error happens
The formal guarantee says you are entitled to a full and immediate refund from your bank or building society if an error is made by the organisation or your bank.
The Guarantee protects the payment instruction, not the whole contract
If the bill itself is disputed
A refund under the Guarantee does not erase a valid bill. You may still need to resolve the underlying contract or usage dispute with the biller.
If it is a card subscription
Recurring card payments are not Direct Debits. Contact the merchant and card provider instead.
What to say to the bank
I am asking for a refund under the Direct Debit Guarantee. The Direct Debit from [organisation] on [date] for [amount] was incorrect because [wrong amount/wrong date/unauthorised]. Please refund the payment under the Guarantee and confirm the reference.