The project manager should try to understand why the customer is not clearing the packages for shipment and not participating in the communication calls. This could indicate a lack of interest, satisfaction, or trust in the project or the project team. The project manager should initiate a dialogue with the customer to address their concerns, expectations, and feedback, and to re-establish a positive relationship. This is part of the stakeholder engagement process, which aims to increase the support and minimize the resistance from the stakeholders throughout the project life cycle. The other options are not appropriate because they do not address the underlying problem and may worsen the situation. Requesting a change in the contract or a delivery date extension may create more conflict or confusion with the customer, and informing the customer that subsequent packages cannot be manufactured may jeopardize the project scope and quality. References: PMBOK Guide 6th Edition, pages 513-514, 518-519, 524-525.