How much do you care about it? Options are: * Let it go. * Keep contacting the founder hoping this is just a misunderstanding. * Be proactive. For option 3

How much do you care about it? Options are: * Let it go. * Keep contacting the founder hoping this is just a misunderstanding. * Be proactive. For option 3 you would want to write down timeline and gather all of the evidence (commit logs, website screenshots, communications with the founder). After that you can let him know that he is using your work without permissions, submit a small claim court case, or talk to a lawyer.