I know exactly my details and they were not entered incorrectly, this message started appearing after I managed to fill out the form the first time and attempted to reset my pokemon trainer account. I never received the email allowing me to update my account information, and since then the "Unable to find an account using the provided information" message has appeared every time.
It was highly frustrating and eventually I decided that the level 6 account was not worth the time attempting to try and contact the management of the Pokemon Trainer accounts as they are backlogged with emails and so decided that the best option was to start again but this time with a Google Account.
Since starting over on a new account I have managed to level up to level 9 and have caught a wide variety of pokemon however I am still looking for Jigglypuff which I managed to capture on my first account.
So if you are seeing this after attempting the reset of your password (resulting in a status quo account that was activated but now not due to pending password change that will never happen to failure of change of password email not being sent) then you are best to start again.
Update 23rd July 2016
It now seems that the creators of Pokemon go are aware of the issue in regards to recovering / updating Pokemon Trainer Accounts and the error message has now changed. I will be trying to continue the recovery of my Pokemon Trainer account however they are limiting connections to the recovery page and it will take some time to sort out. But at least it's progress in the right direction.
Much later in the afternoon I manager's to get through to the email activation page and managed to reset my password by email. I can confirm that my Pokemon trainer account is fully there and managed to successfully reactivated my Pokemon trainer account.