Someone learned how to replace the color blue

This has been bothering me for a while. I have an old freelance client of mine I’ve created an web site for (his company) it was small one so I took the complete payment before deployment and I needed no contract. I deployed the complete version of the site on my server, bought the domain for his company under my name and it has been running for a year now.
Lately he had asked me to give admin privileges to his son (cs student 1y) to upload some photos of their new building. I noticed he ruined several functions on the site in doing so, but I was never paid to support that just the hosting for a year.
When I was making the design I made a simple but pretty logo as a placeholder for the site which went in production since they never gave me company logo. All good, no contract small cash all delivered, everyone happy.
Up until few days when I saw my f**king logo cut out from the site as 250px jpeg and made as a huge banner on the company building..
From my pov I would’ve never given permission to use that since its not something i’m proud of and would suggest to make a better one for a fee. I see this as stolen/unauthorized use of intellectual property. But the laws are super shitty in our country so at this point I am stuck at taking their site, domain a hostage until they pay for the logo they used or take it down or taking legal actions.. we never signed anything about that logo.