I'm not sure from your answer as to what you're doing or where. Sorry about that but I'll need more detail.
Have you signed in to your broadband MyAccount and selected My Services and then Manage TalkTalk Mail?
In My Mailboxes is there any yellow banner error message?
Can you select Add an existing mailbox from the link at the bottom?
And enter the first part of the email address, then select the last part of your email address from the drop-down list and enter the email password and then select the Add button.
Does the mailbox get added to the list of My Mailboxes?
Ah, if the email address is not recognised as a sign in for any MyAccount then maybe you haven't registered for an online MyAccount?
Do you get emails from TalkTalk with billing notifications each month or do you receive paper bills in the post?
If you receive paper bills then the solution is to get one of those bills to find your account number and telephone number and then register for MyAccount.
If when registering for MyAccount you get a message saying you're already registered then if you do receive monthly billing notification emails from TalkTalk then that's the email address you registered for MyAccount.
Understood. That definitely means you should register for MyAccount for online billing notifications to save some money each month and to manage your TalkTalk services.
And having a MyAccount is essential to manage TalkTalk mailboxes.
Thank you for being one of our essential key workers. Stay safe and if you do need any further help then please come back anytime.
I don't recognise the error message.
Dp you get the red banner error message that indicates you're already registered with an email address?
You might need to take a screenshot an upload it here so I can see what you see.
Above this Reply area, the image upload icon is the camera (or picture on a mobile browser) that allows you to upload a screenshot.
If you had mobile data switched off on your phone to ensure you were definitely connected to Wi-Fi and your phone does connect to your home broadband router then that would satisfy the security requirements.
Maybe, further data is required. If so, the TalkTalk team will request that via Personal Messaging here in Community and set up the MyAccount for you including a password recovery email address and mobile phone number.