Unfair Billing Practice

I contacted Schalk van Dyk on Monday 30 October regarding the setup of a contract for the sale of a business. Discussed over the phone with him what I will require of him as well as in email format. He then sent me an quote via email for the work to be done on Tuesday 31 October and required a upfront payment which I did. Upon finalizing the contract on Wednesday 8 November he then demanded more money before he will be releasing the final contract to me. In my opinion this is unfair billing and unprofessional as he never mentioned more money or discussed more money until the final product which I already paid for, is given to me