Unfortunately, some things are learned the hard way. My life has been a nightmare the past week. I'll spare you the details, but if you suspect your identity has been stolen, there are steps you should take IMMEDIATELY.
Put fraud alerts on your credit files. The numbers for TransUnion, Experian and Equifax are all readily available online.
Request your credit reports and review them for accuracy. Look for accounts you don't recognize. Look at the inquiries section for the names of creditors from whom you haven't requested credit.
Report the fraud to the Police. As a victim of a crime, you are entitled to a free copy.
If it's your credit card that has been hit, cancel it.
If it's your debit card that has been hit, cancel it and close your account.
Call your bank, creditors, utility companies, and the DMV if necessary, to alert them to the theft. Follow up in writing with the police report.
If the fraudulent transactions were made over the internet, file a report with the FTC.
If you suspect the thief obtained your information from your mail, report it to the postal inspector. It is also wise to divert your mail to another location or perhaps open a post office box.
Keep track of your phone calls, letters, and all the steps you've taken. You will need to have report numbers ready for vendors and authorities.
I've made 9 pages of notes (so far) of phone calls I've made, reports I've filed, information I've requested... what a mess.
If it's happened to you, good luck.
In the meantime, wish me luck. Ugh.