Great to know you can access your TalkTalk Mail messages on the iPad and iPhone and presumably via an Internet browser on the laptop? Just sign in to your mailbox to confirm that's working ok.
Select here: Sign in to TalkTalk Mail
Enter your full TalkTalk Mail full onetel email address, select Continue and enter the onetel email password, select Sign in.
Now, why are you saying TalkTalk have changed the set up because in practice nothing has changed at the TalkTalk Mail platform.
What's your laptop Operating System and what email software and version are you using?
A screenshot of the incoming and outgoing server settings you have set up would be useful to guide you in. Image edit to obscure the first part of your email address before uploading images here using the camera icon above this Reply area/
