As 4G&5G networks grow in scale and complexity, traditional operations and maintenance (O&M) models—built on alarms, manual analysis, and reactive complaint handling—can no longer deliver the service reliability and experience quality customers expect. Limited fault visibility, slow root-cause localization, and low closed-loop automation lead to prolonged outages, rising OPEX, and declining customer satisfaction. The Agentic AI for Customer-Centric O&M – Phase II Catalyst advances network operations from reactive response to proactive, experience-driven service assurance. Building on the Phase I Catalyst that demonstrated multi-agent collaboration for complaint and fault handling, Phase II extends the scope to end-to-end proactive service protection by introducing a cross-domain service assurance agent and integrating service and network digital twin technologies. The solution establishes an experience-centric, multi-agent O&M architecture aligned with TM Forum Autonomous Network principles. Cross-domain and single-domain agents collaborate through intent-driven workflows covering perception, analysis, decision, and execution. By combining alarms, performance data, XDR, knowledge graphs, large-model reasoning, and digital twins, the system enables intelligent identification, demarcation, localization, and automated resolution of faults and service quality degradation—before they impact user perception. Digital twin technology provides predictive simulation and optimization capabilities, shifting O&M from reactive fault handling to forward-looking service assurance. This closed-loop, agentic approach significantly reduces manual intervention, shortens mean time to repair, and improves the accuracy of experience risk detection, while supporting the evolution toward AN L4 autonomous operations. Success is measured through tangible operational, experience, and business outcomes, including substantial MTTR reduction, lower complaint volumes, improved NPS for high-value users, reduced OPEX, and increased revenue from proactively protected services. By enabling customer-centric, proactive O&M at scale, the Catalyst delivers a practical blueprint for CSPs to improve service reliability, enhance user experience, and unlock greater value from 5G and vertical industry services.