Matthews told the Herald she received a phone call from Aon NZ this morning informing her the company had completed its investigation into whether the person was its employee.
She said Aon NZ confirmed the person was their employee and they no longer work for the company.
Matthews told the Herald she was glad there were consequences for making such comments.
"I was really happy that I had taken action immediately and that I had reported it and that meant that there were consequences.
"I'd like to encourage other people to do the same because these things are designed to make you feel intimidated and not safe, but there are systems in place and I felt like I had a lot of support."
In a statement, an Aon spokesperson said the company's culture of inclusion, diversity and respect were core to its values.
"There is no place in our team for anyone who exhibits behaviours in conflict with these values. As we have previously stated, once Aon became aware of the matter we thoroughly investigated in line with our policies and employee Code of Conduct.
"For privacy reasons Aon is unable to comment further however the person in question is no longer employed at Aon."
The company would not comment on whether the person was dismissed or had resigned.
A police spokesperson confirmed inquiries into the matter are ongoing and no charges have been laid at this stage.
Matthews has previously filed a complaint with Twitter, and it appears the social media giant removed the comment for violating its rules.
The account itself also appears to have been deleted.
"We want to be accountable and available to the public, but nobody deserves to be threatened," Matthews said.
Following the incident late last year, the Herald revealed female councillors have carried personal security devices, had their homes checked by council staff, and felt they needed to look over their shoulders after receiving threatening messages.
Over the years they have felt vulnerable, scared, and intimidated. Many of them feel female politicians are the subject of derogatory comments more than their male colleagues are.