The city is claiming my 4 unit is really a 3 unit. What should I do?

[Trevor Davis]

In 2021 I bought a 4 unit property as my first investment property.  Code enforcement is now telling me I only have a 3 unit property, so I have to kick my tenant out of the newly upgraded unit.  

I got a loan on the property when I bought it.  It appraised as a 4 unit property.  I had it appraised a couple years later and it appraised again as a 4 unit.  I have 4 mailboxes, and signs for all 4 addresses, and I've been paying sewer for 4 units.

I guess I need to set up a protest hearing, but what should I be doing before then?  Do I need to get a real estate lawyer?  If I want to prove my case myself, where should I look?