Carphone Warehouse, Homebase and The Range also received poor ratings in a survey of retailers for the consumer magazine.
Consumer specialists at Which? found these were among the major retailers about whom customers regularly reported poor customer service during the pandemic.
The enforced closure of stores saw a jump in online retail volumes, putting significant pressure on online platforms and introducing some shoppers to digital retail for the first time.
Which? asked more than 5,000 UK consumers who had issues with their order and contacted a customer service team how the biggest online retailers in tech, lifestyle, fashion, DIY and homeware fared regarding issues between March 2020 and March 2021.
JD Sports, The Range, Homebase, Sports Direct, Funky Pigeon, Scan Appliances Direct, Debenhams and Carphone Warehouse were all bottom of the Which? rankings for service, with all averaging one star out of five.
JD Sports and Homebase – as well as Appliances Direct, Sports Direct, Funky Pigeon, Scan, Debenhams and Carphone Warehouse – received one star ratings when specifically asked about helpfulness of staff.
One JD Sports customer said they lost out when they ordered some shoes which never arrived and could not get in touch with anyone in customer service to resolve the issue.
The customer told Which?: “I tried a few times but it felt futile, so I just gave up and lost the £60.”
JD Sports said: “The forced closure of our stores during the national lockdowns stimulated a significant surge in online orders resulting in unprecedented levels of demand across all our online sales channels.
“At the same time, as a direct result of Covid-19 and the requirement to apply strict social distancing measures across our operations to protect the health, safety and wellbeing of our colleagues, we had to reduce the number of colleagues that were working in our various distribution centres and transition our colleagues in customer care to remote working.”
Meanwhile, Marks & Spencer and Screwfix were the top two performers in the survey, with both averaging five star ratings for customer service.
Adam French, consumer rights expert at Which?, said: “The pandemic saw some of the best and worst of customer service.
“But with online shopping now becoming the norm, we should get the same level of customer service when shopping online as when shopping in a store.
“When it comes to spending our hard-earned cash online it is essential we know which retailers we can trust to put right anything that goes wrong.
“With the extraordinary growth in online shopping set to continue as we emerge from the pandemic, retailers who are falling short must up their game to make sure no one is left frustrated and out of pocket because of bad customer service.”