As a business owner, your brand name (or in legal sense, trademark) is probably one of the most important IP assets! If you have registered your trademark, you enjoy the exclusive rights to use the trademark. Unfortunately, you found out that someone is using your trademark without your consent and you want to stop it. You could consider sending a cease-and-desist letter to the infringer to inform your rights and demands.

However, if the infringer does not respond to your notice, you would probably need to consider court actions to enforce your rights such as civil proceedings and injunctions, depending on your needs and situation.