What can I do about defamatory posts about me on social media in the UAE?

What you describe can amount to defamation, and because it is happening online it falls under the UAE's cybercrime legislation as well as the Penal Code — insulting or defaming someone through social media or messaging apps is a criminal offence here, and is treated more seriously than the same words spoken in person. Note that under UAE law a statement can be defamatory even if the person making it believes it is true, so the usual instinct to argue over truth does not work the way it does elsewhere. Start by preserving the evidence properly: keep the original messages and posts on your device, not just screenshots, and note dates, group names and the accounts involved. Then report through the Dubai Police eCrime platform or at any police station; the matter goes to the Public Prosecution, which decides on charges. You can also pursue civil compensation for the harm to your business, either alongside or after the criminal case. Whatever happens, do not respond in kind — a heated counter-post can hand him a complaint against you. A UAE lawyer experienced in defamation matters can shape the complaint and assess a compensation claim on your evidence.