unable to log on

I have been running the paid version on my iPhone 5S and iPad air for ages without any issues, however recently account synching seems to have gone awry so I logged out of my account on both units with the expectation/hope that when I logged back in things might have reset.

Only thing is, now I cannot log in to my account on either device. Works fine when logging on via the website on my PC but on both my mobile devices I enter username and password, click ok but nothing happens. Very frustrating.