This research was conducted with the intention of analyzing “Failure” and “Without Any Respond” types of the incoming calls within an event log before collected from the call center section (i.e., customer service) of a private bank in Bangkok, Thailand. The main idea was to first find and detect the potential and existing problems of the clients and operators hand-ling the customer service incoming calls/contacts, and later find proper solutions to these problems. To do this, we used the Process Mining software Disco developed by Fluxicon company and we applied Fuzzy Miner technique on the collected call center data/event log.