So today I received a Monzo card addressed to someone else… not anyone who lives at our house. They have presumably used this address to apply for an account and even without the monzo card could presumably use virtual cards. I have tried to report this to monzo but their fraud team don’t answer the phone… tried twice and spend more than 30 mins each time. I’m concerned that this person may use our address to commit fraud and this will affect our credit.
If you drop an email to help@monzo.com explaining. Make sure to include the last four digits on the card and the name on the card 
Bit late, but returning it unopened and marked not known at this address should be the usual approach and returned to sender.