A Philadelphia man has said he is considering legal action against Starbucks after an employee asked for his name to label his drink but ended up writing the title of the Islamic State.

Niquel Johnson, 40, told the Washington Post that when he ordered his drinks last week he gave his Islamic name, Aziz, as he had done in the same store “countless” times before. This time, the three drinks he ordered all came back labelled “Isis”.

As well as being an Egyptian god, an alternative name for the river Thames and a song by Bob Dylan, Isis is the common acronym for the Islamic State terrorist group. Johnson said seeing the word on his beverages made him “shocked and angry”.

“I felt it was discrimination,” he said.

In a statement to the Post, Starbucks spokesman Reggie Borges said: “After investigating, we don’t believe this was a case of discrimination or profiling.

“The customer approached and provided the name Aziz. The barista mistakenly spelled it incorrectly. We have connected with Mr Johnson and apologized for this regrettable mistake.”

But Borges’ simple statement belied a baffling, labyrinthine story.

Johnson told the Post Starbucks claimed to have answered a complaint he filed by email via a phone conversation with his niece, Alora.

But Johnson insisted such a phone call could not have occurred. He does not have a niece named Alora and the nieces he does have are too young to have such a conversation.

Johnson provided to the Post a recording of an exchange with a Starbucks representative in which he made clear his confusion and anger.

“So that is a new revelation for me and us, Niquel,” the Post quoted the representative as saying. “And I don’t know how we got to that point. I apologize.”

The Post said the identity of the woman Starbucks says it spoke to remains a mystery.

This is not the first time a Starbucks store in Philadelphia has attracted national media attention, stoking intense debate about race and racism through the interaction between an employee and customers.

Last year, two African American men were arrested after a Starbucks worker in the city called police because the men were sitting peaceably but not ordering anything. The men eventually settled for $1 each and a promise from the company that it would set up a $200,000 programme for young entrepreneurs.

Starbucks’ chief executive, Kevin Johnson, apologised and ordered more than 8,000 stores closed for an afternoon, so that nearly 175,000 employees could be trained about the dangers of unconscious bias.

Johnson told the Post that the outcome of that case made him think Starbucks would treat his complaint seriously.

“You think they would have their facts in order,” he said. “How could they allow anyone to speak for me?”