Please note your email address is capital senstive: if you let your phone suggest an email address, your email address you registered with might have ended up with a capital case at the begining. You can find the original spelling of your email address in the original email we sent you.
This problem is particularly true with Safari users.
Finally, note that if none of these work, you may have signed up with Google. In which case, you will just need to sign-in on the login page with your credentials. Your credentials are managed by Google.
A problem? Message us here: info@doopedoo.co.uk.