Currys PC World is facing a growing number of complaints about cancelled Black Friday purchases, which customers only learned about after the sales period was over.
The firm has blamed a technical fault for causing some orders to fail even though it had sent confirmation emails.
The electronics retailer has apologised for "the inconvenience caused".
But many of those involved want it to go further and to honour the discounts it had offered.
A spokeswoman for the company - which is owned by Dixons Carphone - was unable to say how many people had been affected.
But she indicated the firm would treat complaints on a case-by-case basis.
The issue follows reports of a related problem involving customers being left out of pocket after failed gift card payments to Currys PC World on Black Friday, which was revealed by MoneySavingExpert's news site last month.
In those cases, the company has allowed goods to be repurchased at their discounted prices.
However, it has subsequently emerged that other types of purchases were also affected.
Deals for reduced-priced televisions, computers and speakers are among those shoppers have complained of missing out on.
"I had ordered a 65in TV in the Black Friday sale," Iain Fairfield from Kilwinning told the BBC.
"But it never arrived, so I went onto live chat with Currys and they said that due to a technical glitch the order hadn't gone through properly, even though I had confirmation of it.
"They then informed me that I would have to pay full price for the TV again even though it was a Black Friday deal.
"I was very angry with this as they wouldn't be honouring the original price I had got the item for. And at no point did they ever inform me, from purchase point until delivery day, that the order had been cancelled."
Charlie, another shopper who asked that his surname not be published, said he had a similar experience after a laptop he had ordered was not delivered.
"Glitches happen, everyone understands that. But not offering the goods now at [what was] the advertised price seems wrong," he said.
"What's most irritating is that I would have carried on shopping around on Black Friday had I known the sale hadn't gone through."
In some cases Currys did email users to inform them of the cancellations, but it appears not others.
Incredibly unhappy @curryspcworld my husband ordered a television in the black Friday sale, got a confirmation and it was meant to arrive today. He's just been told the order never went through due to a "technical fault" and we now need to pay full price 🤬— Sarah Boyd (@Sarah8Boyd) December 7, 2020
@curryspcworld hey I have got a receipt of my order placed on 24 Nov, and now I got told it's your tech problem so my order wasn't processed, and I was told to reorder with the original price, why can't you honouring black Friday deals?— Maggie (@FokMaggie) December 4, 2020
The company is now working through complaints, but the extent of the problem is still unclear.
"Due to the unprecedented volume of customers shopping online with Currys PC World on Black Friday, our website experienced a temporary outage," said a spokeswoman.
"We can confirm that transactions made by gift cards and some Order & Collect purchases were affected, but home delivery was not.
"Any customer who paid by gift card had funds put back in full by 20:00 on Wednesday 2 December.
"Those customers whose Order & Collect purchases were cancelled were informed as soon as possible, and they were able to replace their order the same weekend and still take advantage of our Black Friday promotions."
However, the BBC has spoken to four customers who said they were affected after trying to buy products for home delivery without using a gift card.
The firm said it was still looking into the matter and urged all those affected to contact customer services if they still had a proof of purchase.
Consumer rights group Which? has said the electronics store is not legally compelled to offer the cancelled goods at their sales prices, but suggested the firm's reputation was on the line.
"This is the latest in a long list of complaints we've heard about Currys PC World, and customers will be understandably frustrated that their Black Friday purchases could not be fulfilled," commented its consumer rights expert Adam French.
"The tech retailer has earned itself a poor reputation for customer service and in a recent Which? survey received just two stars for its after-sales service.
"The company must up its game or customers will rightly go looking elsewhere for a good deal."