Answer:
A. Let the customer finish complaining, then explain to her why she is having the issue.
Explanation:
In dealing with customers it is important that conflicts is on de-escalation in such a way that the customer is satisfied after the transaction and does not feel bad about the incident.
In the given scenario the customer caused the issue but it is important to listen to their complaint and get clarity on the situation.
Cutting the customer short because a similar situation occurred in the past may not reveal all issues. So it is better to hear the customer's full complaint.
Then we need to explain to the customer why the customer is having the issue without emphasising they are wrong.
This will reduce bad feelings on the part of the customer