Old iPhone unlock fails due to Apple ID 'not valid' error

I am trying to restore my old iPhone, i have connected it to my macbook and done all the steps to restore it. i am now stuck as i have to use an old apple id to unlock the phone. However i cannot do this through the finder prompt as it says my email or password is incorrect. But when i press to reset my passowrd for this account it says:

"This Apple Account is either not valid or not supported"

but yet my old iphone is locked to the exact email address im using to unlock it. i have tried to sign into apple using the same email and apssword and it tells me the account is locked for security reasons, but when i try to unlock it, it redirects me to the password reset page that shows the same error:

"This Apple Account is either not valid or not supported"

Any help would be appreciated as i need to use this phone as a back up whilst my current phone is being repaired.