BT Group PLC (LON:BT.A) and Vodafone PLC (LON:VOD) received the most complaints for mobile services in the UK in the final three months of 2017, according to regulator Ofcom.
Ofcom data revealed the two telecoms giants both had 11 complaints per 100,000 users in the period.
BT also had the highest proportion of pay-TV service complaints with 18 per 100,000 users.
For both mobile and pay-TV services, complaints mainly related to billing, prices, charges and handling.
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In broadband and landline, Talktalk Telecom Group PLC (LON:TALK) received the most complaints with 31 per 100,000 users due to faults and problems with its services.
Sky PLC (LON:SKY), on the other hand, had the lowest proportion of complaints for its broadband, landline and pay-TV services.