Did you pay the full early termination fee and your account balance is zero?
By the way this is different than a locked phone. This is a blacklisted phone. You may want to use that terminology as unlocking a phone is different to help you get what you want from customer service.
Yes, I fully paid early termination fee and my account balance is zero. No, my phone is not blacklisted. After termination of the contract my login was locked and I can not ask for support as the current client. Where in this case, I can write e-mail?