Contract Question

A project is delivered as per the contract by the project team however the customer is not happy.
The customer feels that the deliverable is far below his expectation in terms of quality and functionality and has some serious defects. What should the project manager do in this situation?

a)Talk to the project sponsor to discuss the issue
b)Proceed to project closure activity
c)Discuss the issues with customer and find ways to resolve the same
d)Brainstorm with technical experts, stakeholders and team members to understand issues in the project

Answer given is B
In the question it is mentioned that project is delivered as per contract but can we proceed to closure without the customers acceptance?