Argos has apologised for confusion over prices on toys included in a "3 for 2" offer.
Customers accused the company of pushing prices up as soon as the offer was made available.
But Argos said the toys in question had previously been sold for promotional prices and had now returned to their normal price.
It said it had not clearly marked that some of its toys were on promotion "due to a technical issue".
Cora Harrison wrote a post about the deal on her Facebook page, which went viral.
She said: "A few friends didn't believe that I was getting a good deal so I added some different items to my basket.
"When I came to checkout the next day (when the 3 for 2 had gone live) all the prices had changed."
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Ashley Muir said on Twitter that one item was marked at £29.99 and in store the next day it was up to £45.
The company said: "Before this [our 3 for 2 deal] launched, we ran a promotion on a limited number of toys which we didn't clearly mark as a promotion due to a technical issue.
"These toys have now returned to their standard price and are included in our 3 for 2 promotion.
"We're sorry for any confusion this has caused."