Can’t access account via watch app to set up mobile data after resetting Apple Watch

[Ealham]

I have a data plan for my Apple Watch synced to my phone sim, it was working fine until I had to factory reset my Apple Watch. However, when I now come to set up the data plan again via the Apple Watch app, when I enter the details into the o2 page which comes up, I receive the message'you've entered incorrect details. Please try again and login with the my o2 sign in details associated with this number.' The details I'm entering are correct. I've entered the same details on the o2 app and multiple web browsers and the details allow me accesss to my account. I've changed the password and again after changing the password, it will let me sign into my account everywhere apart from the watch app to enable me to set up the mobile data plan. Both the phone's and watch's software is up to date and turning both on and off again has not helped. Please help so I'm actually receiving the service I'm paying for. Thanks james. 

[MI5 · Accepted solution]

@Ealham 

Customer service need to remove the watch from your account so you can start over with the registration process.

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