Someone did the same thing with my GMail to sign up for an Apple account. Of course I already own the account with my GMail; however, you can add periods anywhere in the address or add "+tag-name" and it all goes to the same place. So the following all route to the same address.

firstnameLastname@gmail.com

firstname.Lastname@gmail.com

firstnameLastname+tagname@gmail.com

So there are infinite permutations of your address that could be used even if you are successful in blocking your default address. Most systems including Apple don't recognize these as the same address.