Did you register at both .com and .co.uk? They are different domains. Just because you are registered at one does not mean you automatically have an account at the other UNLESS you registered at both. If you did this, you would have two different emails. Mail sent to .com would only go to your .com inbox and .co.uk would only go to your .co.uk mailbox.
If it is not recognizing your password and saying the security question is wrong
which you did not provide, it's highly likely that you have been hacked. Try the steps
HERE to regain control of your account.