An Exeter woman said she was left "choked up" and "embarrassed" when a Marks and Spencer employee did not recognise her hidden disability.
Tay Beales, 22, was shopping with her girlfriend Freya in Exeter when she needed to use the disabled toilet at Marks and Spencer.
She claims she was turned away by staff who, despite her having epilepsy, said she was "not disabled".
Marks and Spencer has apologised for the incident.
The 22-year-old said she was also misgendered by the worker and told to use the men's toilets.
Tay said: "The M&S woman was standing in front of the disabled toilet and so I opened the handle and she sad 'no, no, no, you're not going in there - you're not disabled'.
"I said to her 'I am disabled, I have epilepsy'. A sign on the door even said that 'not every disability is visible'.
"Then she told me 'no, you need to go in there' and shooed me into the men's like cattle. I didn't know that I was going into the men's at this point. I got in there and there was a man having a wee."
Freya said: "I could hear the customer talking to the employee and the customer said 'I can't believe you have let a man into the toilet'.
"The staff member then said 'she's not a man and I didn't know where to put her, she said she's disabled but she's not'."
Tay said: "We went and spoke to the manager who apologised. It was only after we told the manager that we were going to make a formal complaint, did they take my contact details.
"I don't think the manager took the incident seriously."
Tay added: "The whole thing was contradicting, as there was a sign on the door to say not all disabilities are visible. We are in 2022 and I want people to be more aware of this."
A video about the incident on TikTok has been liked more than 40,000 times.
A spokesperson from M&S said: "We have a zero tolerance approach to discrimination across M&S and we always work to ensure that our stores are welcoming for everyone.
"We are very sorry that Tay’s experience did not meet the high standards of customer service that we set for ourselves, and for the upset that this caused.
"We have spoken today with Tay to apologise directly and she has accepted a gesture of apology.”