MEXICO CITY - Mr Rogelio Villarreal knew nothing about French jeweller Cartier, he said, when an ad popped up on his Instagram feed in December. He clicked on it, perusing the pages of bling and other luxury items, including handbags, watches and necklaces, each listed for thousands of dollars.

Then Mr Villareal, who lives in Mexico, noticed a pair of earrings: slender studded 18-carat rose-gold cuffs lined with diamonds, priced at just 237 Mexican pesos (about US$13 or S$18).

He bought two pairs. Later, the price for the earrings was adjusted on the Cartier website to 237,000 pesos – more than US$13,000 (S$18,000).

The purchase initiated a monthslong tussle between the surgery resident from the northern state of Tamaulipas and the storied brand, with hundreds of social media users following along – some cheering, others taunting – and even a Mexican senator weighing in on the dispute.

“I was amazed to see how much the necklaces cost and so on and I said: ‘Someday,’ until I saw the earrings,” Mr Villarreal, 27, wrote on social media. “I swear I broke out in a cold sweat.”

Within a week of the purchase, Mr Villareal said, Cartier began a series of attempts to cancel the order, initially saying that the earrings were not available.

When Mr Villarreal made no move to cancel the order, he started receiving phone calls from company representatives.

They told him that “the earrings that I had ordered were not at the correct price, which is why they wanted to cancel the purchase, and that because of the inconvenience they would give me a gift,” he said.

As “compensation”, the company then offered “a gesture from the house of Cartier” – a complimentary bottle of Cartier Cuvée Champagne and a leather Cartier item, according to an e-mail sent to Mr Villarreal.

He decided to reject the gifts and fight back, using a contact form on the company’s website to cite a federal consumer protection law in Mexico that says that a goods supplier can be taken to court “by not respecting the terms and conditions under which” a product or service is purchased.

Cartier has not responded to several requests for comment.

Mr Villarreal found the terms and conditions for sales on Cartier’s website in Mexico, which state that any dispute could be brought to the Office of the Federal Prosecutor for the Consumer for “conciliation”.

So he did just that. He filed a complaint with the Matamoros branch of the federal consumer protection agency.

The agency, which has a role similar to that of the Federal Trade Commission in the United States, has a history of intervening on behalf of consumers when retailers change list prices after a sale.

In February, the consumer agency invited consumers to join a class-action lawsuit against Sony, which had cancelled orders for a PlayStation 5 console that it had offered on its website in Mexico for a 30 per cent discount.

The consumer protection law is so well known in Mexico that people use social media to draw attention to erroneous prices on Amazon and other retailers’ websites in posts that are widely seen and shared, according to El Economista, a newspaper in Mexico City that covers financial news.

Mr Villarreal said that the consumer agency had summoned Cartier for arbitration and that the government had made several attempts to mediate an agreement. Agency officials said they could not share information about an open case with anyone other than the parties involved.

If the consumer protection agency finds that a company is at fault, it can impose fines or other penalties, but it can’t force a company to abide by a price it listed, said Mr Jorge López Zozaya, a corporate lawyer in Mexico City. If no agreement is reached, either party can ask for a judge to resolve the complaint.

Mexican law does not extend protections to consumers if a listed price was clearly a mistake, Mr Zozaya said.

“If this case had gone to a court of law, it probably would have resolved favorably for Cartier,” he said.

But there appeared to be a truce in the matter. Before a consumer agency mediation hearing this week, Mr Villarreal said that he had received notice from Cartier that his order would be fulfilled. The agreement could not be confirmed with Cartier or the agency.

“War is over,” he wrote in English in a social media post.

Some users applauded his tenaciousness in getting Cartier to comply with the terms of his purchase, while others, including a Mexican senator, accused him of abusing the consumer protection system for his own gain.

“It is wrong to take advantage of a mistake to the detriment of another person,” wrote Ms Lilly Téllez, a senator from the state of Sonora, adding, “even if the law supports you.”

Mr Villarreal said that he was happy that the ordeal appeared to be over but that the legal process would continue until the earrings arrive. NYTIMES