Well, I have resolved the problem myself so I thought I'd share the advice I was given. Firstly, I rang the Department of Fair Trading. They told me that since the landscaper was unlicensed there was nothing they could do for him if he wanted to ask for more money. In fact, since he is trading without a licence he is in breech of the building laws and could be fined himself. They did however caution me that he could seek legal recourse elsewhere, eg the small claims court. They recommended that I contact him in writing to say that we wished to terminate any agreement we had with him. Secondly, we rang a solicitor and managed to get some (free) advice over the phone. He told us to write to him, either by email or post (not text message) and state that we have discovered that he is unlicensed and, therefore, must terminate our agreement with him. He also recommended that we add that if he does have a licence it should be produced by the end of the day 5pm. The necessity of this second part was apparent when the tradie said, typically, that his licence had only just expired. This wasn't true - Dept Fair Trading told us it had expired in 2016! Also, he said, he had the paperwork at home and would have licence the very next day. Yeah, right. (It doesn't take much to go from trusting to cynical!) Interestingly, although the Dept of Fair Trading recognised there was no contract (there should be a contract and licence for every job worth $5000 or more), the solicitor seemed to think a verbal agreement might still have some value. We did as he recommended. The tradie, fortunately, agreed to terminate and that was the end of that. We did pay him more than we probably should have but we were glad to get out of that mess.