I paid for custom work and no-one is responding to my emails now

I requested custom modifications to the plugin. I was told they could make the changes for me and all I would need to do is subscribe to the pro version and verify the changes. This was a generous offer, which I accepted. I approved the changes I was requesting in November and since then no-one has returned any of my emails. I have also set emails to the owner herself as well as text messages and still no response.