Concerned customer

We had a traumatic experience with Mark. He was helping us with a project and there was a lot of back and forth with the city. After we had received the permit from the city, we needed one more form signed off. Mark became completely belligerent, ignoring our texts, and when we finally got him on the phone he cursed at us, used inappropriate language, and refused to complete the work. We followed his advice every step of the way and made all of the changes he requested. We understand if there are differences of opinion, but speaking to customers in a vulgar and threatening way is unacceptable.