After sending two invoices for payment, I sent another and called the client when the receipt that they had received it came back. 

Client: Why are you calling me? 

Me: You haven’t paid and this is the third invoice I’ve sent. 

Client: It’s even more than the last one!

Me: Yes. The contract you signed stated that I would add a late fee for payment. 

Client: You mean I have to actually pay you? I thought you were joking!

Me: What on earth made you think that? 

Client: You’re a freelancer!

Me: And…

Client: Well, you work for free! If you were supposed to be paid, you’d be called a paidlancer or something!