NEW DELHI: Telecom operator Bharti Airtel lost 5.7 crore mobile customers in December 2018, according to a company statement released Thursday.Its mobile customer base in India at the end of December 2018 stood at 28.42 crore.According to subscriber base report of telecom regulator Trai, Airtel had 34.1 crore mobile customers at the end of November, implying the company lost around 5.7 crore customers in December.With this decline, the gap between Reliance Jio and Airtel customer base narrowed in December. Jio reported total mobile customer base of 28 crore by the end of December.Airtel, however, witnessed rise in 4G customer base. Overall, 4G customer base stood at 7.71 crore at the end of the quarter.