"How can I buy my frozen food and fresh vegetables and fruit from this company?" Mel Jones wrote. "Sorry, you have not replaced 'like with like',"
Hampsta general manager Gary Alway said the partnership with Countdown was dropped after they failed to agree on commercial terms.
"We're dealing with everyone on a case-by-case basis. The supermarket category isn't the biggest category we have.
"The Facebook [page] is going mental, we're dealing with about 12 complaints - they've actually contacted us and are really unhappy and we're dealing with them."
Refunds would be awarded to some customers, Mr Alway said.
"Yes, there's some upset people but the majority of them didn't spend a lot of their money at Countdown."
Customers could also purchase meat, eggs, milk and bread at the Mad Butcher stores, another Hampsta partner, he said.
Commercial breakdowns "happen everyday in business", Mr Alway said.
He did not rule out a partnership with another supermarket chain in the future.
"We've got tens of thousands of customers, there's 49 posts on the Facebook page, it's not big."
In an open letter to Hampsta posted on their Facebook page, Keri Carnie formally requested a refund of her money.
"I continued with my Hampsta this year on the belief that I could use Countdown for my grocery shopping.
"You've not been open and honest with me as a customer as to what was going on and from my perspective, you've acted in an underhanded and sneaky manner by not notifying me about Countdown no longer being available and hoping to get another supermarket in before I noticed.
"If I need something from the supermarket I could have gone down the road and got it not waited and paid for delivery.
"That's why I used your card instead of the supermarket savings scheme. I've learnt my lesson for next year.
"I would like my money refunded as I entered into an agreement with you based on your suppliers at the time.
"You breached that agreement by not retaining that supplier.
"You have orchestrated this in a terribly manner and your conduct has lead me to believe that I can no longer trust you as a business with my money."
In a statement posted on its website, Countdown said: "We regret to inform you that Hampsta have decided to remove Countdown from its list of redemption partners. As a result, customers will no longer be able to purchase their groceries at Countdown by using their Hampsta card".
