Costco has been planning its big credit card changeover for months, but it hasn’t gone smoothly for all customers.

On Monday, Costco officially dropped its longtime exclusive partnership with American Express and began accepting only Visa cards, including a new, co-branded Costco Anywhere card issued by Citigroup.

Customers who previously had Costco’s co-branded American Express card were supposed to receive their new Visa cards in the mail automatically. But since Monday, dozens have posted complaints to the wholesale club’s Facebook page complaining about problems with the switch-over.

Several said the new credit cards never arrived, but their Costco American Express cards were canceled on schedule and they had trouble getting help from Citi customer service.

Some customers complained about long hold times. Other complaints concerned improper balances and new cards not working.

Although Visa is now the only credit card accepted at Costco, members can use other forms of payment or Visa cards other than the Costco Anywhere card, but only the co-branded card gives shoppers cash-back perks that are slightly higher than those offered with Costco’s American Express cards.