The complaints in the case of Bharti Airtel mostly came from 2G pre-paid subscribers in Tamil Nadu (including Chennai), Kolkata, Haryana and Jammu and Kashmir, where the benchmark violation ranged between 0.11 percent and 0.12 percent.
According to quality of service norms, the complaint level should not be more than 0.1 percent per 100 bills issued in one quarter.
The maximum violations are found in the case of Vodafone, where 0.15 percent and 0.13 percent of bills were disputed by its users in Andhra Pradesh and Karnataka, respectively.
Vodafone is the only company during the reported quarter whose post-paid customers in the Mumbai circle also raised a number of quality issues.
Complaints against Idea in the north-east telecom circle pertained to 0.13 percent of disputed bills.
As for other quality parameters, TRAI found performance of Aircel below par for call drops in most telecom circles.
TRAI has set a penalty of up to Rs. 2 lakh for poor mobile service, including call drops. The penalty kicks in for more than 2 percent call drops in a quarter in one telecom circle.
According to the report, Aircel's 2G network crossed this limit in four circles. The call drop rate on the Aircel network was as high as 27.73 in the north-east circle. Airtel, Sistema Shyam and Reliance Communications (GSM) service also overshot the call drop level in one circle each.
During the peak hour, the rate is relaxed up to 3 percent. Even in this category, the figure remained above this level for Aircel 2G in 11 out of the 22 telecom circles.
State-owned BSNL, Tata Teleservices (CDMA) and Vodafone also failed on the 3 percent parameter in one circle each.
Telenor's performance was found below par in Bihar and UP East circle, as per the report.
RCom topped the list of offenders in the deposits refund category, followed by Tata Teleservices. As per TRAI rules, a telecom operator should refund 100 percent of the claimed deposit within 60 days, but RCom, including its subsidiary, breached this norm across 20 circles in the country.
TTSL did not comply with the deposit rule in six telecom circles, according to the report