What should i do if someone used my social security number?

For official guidance in the US this is the safest starting point: https://www.identitytheft.gov/. It’s clear and surprisingly easy to follow.

If this happened outside the US or you’re not sure SSNs apply in your country still follow the same principle: lock down financial accounts change passwords and file a police or cybercrime report. Laws vary but early reporting always helps.

If your Social Security number has been misused act fast. First place a fraud alert or credit freeze with the major credit bureaus so no new accounts can be opened easily. Then review your credit reports for any accounts or activity you don’t recognize.

You should also report the identity theft to the relevant authority. In the US that’s done through IdentityTheft.gov which walks you through recovery steps and creates a report you can use with banks and creditors. Keep records of everything and don’t ignore small suspicious charges.