MEXICO CITY, (Reuters) – Mexicans have been overcharged $13.4 billion a year for phone and internet services as the industry dominated by billionaire Carlos Slim gouges customers and keeps the economy from growing, a study released yesterday said.

Mexico, the second-largest economy in Latin America, cannot reach its growth potential until the cost of phone and internet access comes down and more people have easy access to telecom services, the report from the Organisation for Co-operation and Development said.

From 2005 to 2009, Mexican consumers paid $13.4 billion a year excess for phone and internet services, with high fees disproportionately hitting the poor, according to the report. In total, overcharging cost the economy $129 billion over the five-year period, the report found, nearly 2 percent of the country’s economic output.

“Inefficient telecommunication markets impose a significant cost on the Mexican economy and the welfare of its population,” according to the report that reviewed the country’s telecom sector.

Mexican home phone service is dominated by Slim’s Telefonos de Mexico, or Telmex, which provides about 80 percent of services while the billionaire controls about 70 percent of the cellphone market through his America Movil.

“This is a critical study…that exposes the weakness of the telecommunications sector in Mexico,” Dionisio Perez-Jacome, minister of Communications and Transport, said at a press event accepting the report.

The report found Mexico had the lowest per capita public investment in telecommunications in the 34-member OECD, while Slim’s Telmex had very high profit margins compared to other countries.

In 2008, Telmex had a profit margin of 47 percent, while the average for countries including Canada, the United Kingdom and the United States was 28 percent.

A Slim spokesman declined to comment on the findings of customers being overcharged, but pointed to other reports that Mexico enjoys a relatively-affordable broadband base.