Last year, Costco Wholesale Corporation (NASDAQ:COST), the world’s largest wholesale club, announced it would be ending its 16-year relationship with American Express. A dispute over card fees was at the heart of the matter. Costco switched from American Express to Visa on Monday. All accounts were supposed to have been transferred from American Express to Citi by that date.

Costco now accepts all Visa cards. Costco’s American Express cardholders were supposed to have received their new Costco Anywhere Visa Card by Monday. The Costco Anywhere Visa Card offers cardholders 2 percent cash back on Costco purchases.

The launch turned into something of a nightmare for the company. The rollout drew hundreds of complaints on Costco’s Facebook page. Citi’s Twitter feed was also full of comments from angry Costco customers. Citi had received 1.5 million customer calls by late Wednesday.

Some customers complained that they hadn’t received their new cards in time. Others were unable to activate their new cards. Long hold times for calls to customer service at Citi and Costco made many of the company’s customers furious. One Costco customer on the retailer’s Facebook page said that she was on hold for three hours waiting to talk to Citi’s customer service.

Costco said on its Facebook page, “Due to high levels of interest in the Costco Anywhere Card and high volumes of calls from cardholders, callers to Citi should expect longer-than-desired hold times. Citi is reviewing processes and pulling in additional resources to alleviate hold times.”

Costco said wait times had dropped from 30 to 40 minutes on average on Monday to less than 10 minutes late Thursday. Citi has increased the number of customer-service representatives taking calls to more than 2,000.

A spokeswoman for Citi said that more than 11 million cards had been sent to existing Costco card members. Two-thirds of the cards have been activated. Roughly 180,000 customers didn’t get a card because it was mailed to the wrong address. Citi is now resending those cards to the proper addresses.

The move to Visa is expected to save Costco a lot of money. Roughly 25 percent of Costco’s sales were made using the AmEx card, which carried a fee of 0.6 percent. This meant that Costco was paying American Express about $180 million a year in card fees. The switch to Visa, with fees of 0.1 percent to 0.4 percent, will save the company$60 million to $150 million a year.

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