Simple.

Call the police and file a report that you received the email and did not stay nor was even in the said city at that time and are concerned of false identity and possible resulting actions. Shouldn't take too much of your time and will protect you if something does happen. ie. credit issues, damage scenario.....and if it does, you can then proceed with legal action.

Notify corporate consumer affairs of the event and that you have filed a police report.

When the police follow up, the GM will likely actually do something about this.