Rogelio Villarreal knew nothing about the French jeweler Cartier, he said, when an ad popped up on his Instagram feed last 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. Villarreal, 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, or about $13.
“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.”
He bought two pairs. Later, the price for the earrings was adjusted on the Cartier website to 237,000 pesos — more than $13,000.
The purchase initiated a monthslong tussle between Mr. Villarreal, a surgery resident from the northern state of Tamaulipas, and Cartier, with hundreds of social media users following along — some cheering, others taunting — and even a Mexican senator weighing in on the dispute. But Mr. Villarreal said on Friday that he had received the earrings for the steeply discounted price and noted that he had a special person in mind to be their recipient.
“I’m excited,” he said, “especially for my mom. Those earrings are for her.”
The sweet deal did not come without some resistance.
Within a week of the purchase, Mr. Villarreal 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.
He said 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.”
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 email 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 canceled orders for a PlayStation 5 console that it had offered on its website in Mexico for a 30 percent 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 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,” Mr. Zozaya said.
But there appeared to be a truce in the matter. Ahead of a consumer agency mediation hearing next week, Mr. Villarreal said on Monday that he had received notice from Cartier that his order would be fulfilled, and then announced the earrings’ delivery on Friday. The agreement could not be confirmed with Cartier or the agency.
“War is over,” he wrote in English in a social media post on Monday.
Mr. Villarreal said on Friday that the earrings arrived, and he shared a photo of two small boxes wrapped in paper with wax seals. “Once upon a December,” he wrote in the 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, had 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 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 was over and that he would sign an agreement to settle his complaint with the consumer protection agency.
Elda Cantú contributed reporting from Mexico City.