Calling Matthew a Cohen when he is recorded as being a Levite shows a rather low level of literacy on your part, It squares with recognizing Matthew as the only literate disciple and then citing Paul.
That said, the quality of the defenders that his New Zealand eminence has attracted speaks to the quality of his position.
The low level of literacy is yours alone! The original Gospel of Mathew written in his native tongue made it plain that he was a cohen. Paul's words in ver. 24 were taken therefrom. subsequent verbiage is of questionable origin. .
http://www.jewishanswers.org/ask-the-rabbi-1586/cohen-levi-and-yisroel/
“Thank you for your question. The Jewish nation is divided up into 12 tribes (the children of each of Jacob’s 12 sons). One of these sons is Levi, and a subgroup of Levi is Cohen.”