| If your client called you for service, it is his responsibility to ask you for an estimate prior to your doing the work. If what you state here is how everything transpired, you are owed for the work you performed. He called you to perform the service, and you performed it. So how can he state that he did not authorize the work? If the amount of your bill is in question, then he should be discussing that with you, not denying you payment.
If your client refuses to acknowledge that he owes you any money, depending on where you live and the amount of the bill, you are allowed to sue him for your money in small claims court. Most small claims courts allow people to file a claim that is worth $5,000 or under. You do not need a lawyer. You just need to be able to verify that work was performed at his request. I believe a copy of your phone records showing the phone calls you received from him, in and around the time of the work performance, should be proof that he did contact you. Include copies of your bills to him. It will be up to a judge to decide who is lying about this. | 
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