The mobile operators Vodafone and EE are failing on the basics of customer service, according to the consumer group Which? Of the big firms, Vodafone and EE scored the lowest in a survey which compared all the UK's mobile suppliers. They scored particularly poorly when it came to ease of contact, and value for money. Vodafone promised improvements over the coming months. EE said it was transforming its customer service. "Our latest survey once again shows that the major mobile providers are still failing on the basics of customer service," said Alex Neill, director of campaigns and communications. "Telecoms are an essential part of modern life and so providers need to start delivering for their customers," she said. Both companies came bottom in a similar survey a year ago. Is this a case of diseconomies of scale for these two big companies? For the second year in a row, the online provider Giffgaff, which does not have any shops or call centres, came top of the table. Vodafone apologised, and said it was working hard to improve the customer experience.