I suffer from mistaken email identity all the time - pretty much every week.
I signed up for an Apple @mac.com email address on the day the iTools service was released back in January 2000. Because I was early I managed to get the short-form of my firstname @mac.com (for example <firstname.lastname@example.org> - it's not that though).
As the iTools service morphed into .Mac, then MobileMe and now iCloud, I have also gained the same username @me.com and @icloud.com.
Now it seems, everybody who shares the same first name as me, thinks one of these email addresses is theirs. So I get online shopping confirmations, flight and hotel bookings, Netflix signups, PlayStation Plus and Xbox Live subscriptions, medical appointments, mortgage approvals and everything else you can think of.
In the past, I've often been able to contact the organisation, explain and have my email address removed. But since GDPR they often want me to confirm some account details I don't have just to contact their support or customer services.
So, in such cases, my only option is to request a password reset, login, and either close the account, or change the email address to something else.
I think every email sign-up should require people to confirm their email address before allowing them to proceed, and the confirmation email that is sent should have an "I didn't signup, remove my email address" option. Currently, hardly any do this.