I'm building a house in Washington state. I consulted an engineer because the city forced me to. The engineer never provided a bid or contract but did the work anyways. He did way more than what was asked of him and what he did was not to the specifications I asked for. He also screwed up some calculations and incorrectly sized some beams. When I found these mistakes I fired him an did not pay his bill. The job was only supposed to be for a few areas of the house plan that the city wanted clarification on. His bill was about $6k. I have never paid more than $2k for an entire house plan before. I told him directly that what he did was more than I asked and out of the scope of work I wanted and that he screwed up many parts of it and his screw ups cost me more than his bill also he created design challenges I couldn't fix and for those reasons I wasn't going to pay him anything. He sends me a bill by email every month and includes interest too. What should I do? Just keep ignoring it and him or what. Thanks Brad