Keeping mobile phone bills down is a crucial way to regulate your spending, but if customer service representatives are unable to answer basic questions, customers could find it hard to make comparisons between different providers.

A mystery shopper asked each of the UK’s major providers a series of questions about peak and off-peak rates and international roaming costs during 100 telephone calls in January and February.

According to the survey, staff at O2 were the most likely to be caught out by a tariff question, with four in ten questions answered with inaccurate or inadequate price information.

Virgin Mobile outperformed competitors, with staff offering the highest proportion of accurate information.

The runners-up, in order of accuracy, were 3, T-Mobile, Orange and Vodafone.

But O2 spokespeople insisted that the survey had drawn sweeping conclusions from a limited study.

“We continue to invest heavily in making sure that our customers receive the best possible service,” an O2 spokesperson said.

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