Solve a real-world churn problem with Machine learning (including a detailed case study)

Customer churn is a major problem for most companies. Losing customers requires gaining new customers to replace them. This could be around 10X more expensive than retaining existing customers, depending on the domain. A customer is considered churn when he/she stops using your company's product or service. This is easy to define for a contractual setting, as a customer is considered as churn when fails to renew the contract.