The business process owner should own the risk of customer data leakage caused by the service provider, as they have the responsibility and authority over the design, execution, and performance of the business process. The business process owner is also accountable for the risks and controls associated with their process, and they can provide valuable input and feedback on the likelihood and impact of customer data leakage on the process outcomes and objectives.

The other options are not the best choices for owning the risk of customer data leakage caused by the service provider. The service provider is responsible for delivering and supporting the billing function and ensuring the security and privacy of the customer data, but they may not have the full visibility or understanding of the business process and objectives. The vendor risk manager is responsible for managing and monitoring the vendor relationship and performance, but they may not have the direct involvement or influence on the business process and its risks and controls. The legal counsel is responsible for providing legal advice and guidance on the contractual and regulatory obligations and implications of the outsourcing arrangement, but they may not have the detailed knowledge or experience of the business process and its risks andcontrols. References = Guide to Vendor Risk Assessment | Smartsheet, IT Risk Resources | ISACA, Data Ownership: Considerations for Risk Management - ISACA