I trade on Cex and I've had some difficulty logging on in the past due to their 2-factor login authentication. I reported the issue on their blog since I couldn't sign in to their Support Centre. Within 2 days, an administrator replied asking me to send an email from the address I signed up with and to provide as many details as I could about the account, such as balances, account creation date and so forth. They then disabled my 2-factor settings for me. Perhaps you should try this.