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Rapayet Pushaina thinks he is about 80 years old; he is pretty sure he was not born on 31 December, and he is absolutely certain his name is not Iron Scraper.

But that is the information that appeared on his Colombian national ID card for more than 50 years.

Pushaina, an elder of his clan of Wayúu Native Americans, who live in the deserts of the north-western Guajira peninsula, chafes at the mockery of a name that was given to him by an official of the national registry office who went to his remote village 50 years ago.

"I don't want to be Raspahierro [Iron Scraper], I am Rapayet," he said through his Spanish-speaking granddaughter.

He is one of thousands of Wayúu Indians who were given derisive names, according to Estercilia Simanca, a Wayúu lawyer.

"In some cases there may have been a misunderstanding but in others it was clearly intentional," she said.

Wayúu ID cards show names such as Arrancamuelas (Tooth Puller), Bolsillo (Pocket), Cabezón (Big Head), Chichí (Piss), Coito (Coitus), Gorila (Gorilla), Monja (Nun), Payaso (Clown) and Teléfono (Telephone).

Others are Alka-Seltzer, Land Rover, Marilyn Monroe and Tarzan.

Most neither speak nor read Spanish so were unaware of the mockery. The Wayúu native tongue is an Arawak language.

They do not use the Gregorian calendar either, but rather mark dates with knots on a yarn. Because of this, registry officials opted to give everyone the same birth date: 31 December.

"Since I was little, I thought it was strange that all my family had the same birthday," Simanca said.

She has conducted an investigation into the apparently widespread practice of making up names and birth dates and estimates about 70% of Pushaina's generation were given humiliating names by visiting registry officials, and nearly all were listed as having been born on 31 December.

Pushaina only became aware of his "official" name when he began to attend meetings with NGO and government officials about 10 years ago as a representative of his community.

"At first I thought they were pronouncing my name wrong," he said. Then he realised that what was on his ID card was a twisted joke.

Film-maker Priscilla Padilla has documented the abuses in a documentary called Born on 31 December, which was screened last month in Bogotá.

The Colombian registry office has said it does not know how or why the changes to names and birth dates – the bulk of which happened in the 1960s and 70s – were made, and has promised an investigation.

The director of the office, Carlos Ariel Sanchez, vowed to "correct the names that make people uncomfortable or that are ridiculous".

Simanca said she was encouraged by the official statement but that name changes were too costly for most Wayúu, who live in remote rural areas and can hardly afford travel and legal costs which can add up to more than 200,000 pesos (£67).

"Just like they have ID card drives where they go from village to village registering people, they should send out officials to rectify the names," she said.

Pushaina is now privileged among his clan. With the help of Simanca and Padilla, he was able to reclaim his true name.

He says he is happy with his new card. "Now no one can make fun of me any more."