Amazon is continuing to investigate after high-value orders were switched for cheaper products before delivery.
Items such as cameras, watches and mobile phones were replaced with cat food, condoms and balloons, a BBC investigation has shown.
Some victims were denied refunds until the broadcaster put their complaints to Amazon.
It said it was "working tirelessly" to make changes to processes so it could improve customer experiences.
More than 40 people got in touch with the BBC in response to the story of a Salisbury man whose £1,400 camera and lens was swapped for cat food.
One customer was Annabell Kesby, from Leeds, who ordered a Google smart watch for £380 in March.
Refund requests
"I opened the box to find condoms," they said. "I called Amazon to complain and they sent me an e-mail saying that I had made a large number of refund requests, so they were investigating my account.
"I felt as though they were labelling me as a criminal and a liar."
Ms Kesby who has autism, said she suffered several panic attacks and sleepless nights, after they were told they would not be getting a refund.
After the BBC put their complaint to Amazon, they offered a refund.
Sumit Malhotra, from London, received a pack of balloons and stickers after she ordered a £2,000 MacBook Pro computer from Amazon in February.
"I really freaked out when I saw the balloons," she said.
Complained
"I phoned Amazon to complain, but they didn't take me seriously."
Ms Malhotra was told by Amazon she needed to wait until its own investigation was complete before she could be refunded.
Amazon said it had since offered her a refund.
"Customer satisfaction is our utmost priority, but we recognise we're not perfect," a spokesperson said.
"We are sorry that these customer experiences did not meet the high standards we expect."
Another customer, Harry Wilson, a doctor from London, ordered a Samsung Galaxy laptop for £500 in January.
Colouring book
He received a parcel containing greaseproof bags and a child's colouring book.
"I sent multiple e-mails to Amazon, and they essentially concluded that they were not responsible because I had given the one-time pass code to the driver," he said.
"Overall, I sent more than 30 e-mails to Amazon, and spent hours on phone calls," Dr Wilson said.
"I am an NHS worker, so I really do not have so much time to waste."
Matt Haywood, from Cornwall, ordered an iPad and keyboard for more than £400 last year.
He received a toy digger and some plastic toy building plates.
"I was absolutely fuming and was left out of pocket while they investigated it," said Mr Haywood. "I eventually received a refund after lots of complaining."