Invoice not paid by buyer and not responding to messages

Hi,

So my client told me that he needed 5 videos for the project when it clearly mentioned only one in his proposal. And he told me this after accepting my proposal so I have nowhere to go. 

I agreed for the time being and made him the video. After I sent him the video, he has not responded to any of my texts for 20 days. I have sent him invoices, still no response.

Kindly look into this and help me with this issue. Its really frustrating