A man says he has been told by NHS Test and Trace that he has coronavirus - despite never having taken a test.
Alex Weedon, from Colchester, said his details had been confused with at least two other people called Alex.
His home address was shared with at least one other person, he said.
The Department for Health and Social Care said NHS Test and Trace was processing about 280,000 tests a day with the "vast majority of people reporting no issues with the process".
It said it could not comment on individual cases but in a minority "an individual may order a test via email but we may not have the correct phone number, or vice versa".
Landscape gardener Mr Weedon said he received an email from NHS Test and Trace on Monday, saying he had tested positive.
"I thought 'I hadn't even had a test, what's going on here?' so I phoned the 111 service and she confirmed that the email address it had come from was correct," he said.
"When I clicked on the link, it came up with a different Alex, a similar date of birth except for the month, my NHS number, my email address but a completely different phone number."
The 35-year-old said he was "puzzled" and his partner Melissa Kelly phoned the mobile number that was on the form.
Mr Weedon said: "It turned out to be an Alex from London who unfortunately had tested positive for Covid and he had been contacted by test and trace asking him if it was me, with my home address and everything.
"But he was a completely different Alex to the Alex who was on the form. There were three people called Alex involved: one who has Covid, me - and I've not even had a test - and we can't find this other Alex at all. It's very baffling."
NHS Test and Trace has been criticised for being less effective than local public health teams.
Earlier this week. Martin Usborne, from east London, and his wife Ann said they were bombarded by NHS Test and Trace, receiving more than 60 calls.
Earlier this month, a technical glitch saw 16,000 Covid-19 cases go unreported in England and close contacts of those who had tested positive going untraced.
According to the Department of Health and Social Care, NHS Test and Trace has reached more than 900,000 people since it was started.
The first week of October saw the service successfully reach 76.8% of people who tested positive and 76.9% of contacts where communication details were provided, the government said.