Yes. Your customer can cancel their Direct Debit mandate at any time by contacting their bank. This is their legal right under the Direct Debit Guarantee.
What happens when they cancel
NRTH is notified through BACS within 1 to 3 business days. The customer's mandate status will update to inactive in your Customers page.
Once cancelled, no further payments can be collected from that customer. Any pending collections that haven't been submitted yet will not go through.
What you need to do
If you still need to collect from that customer, they'll need to sign a new mandate. You can send them a fresh invite using any of the four invite methods (Share, Add, Email, or Import) and once they sign, you can start collecting again.