Thanks for your post and apologies to hear that your mum is having issues with her phoneline.
As it stands, we are moving all customers over to a landline that is provided via a broadband connection now. Full areas are being migrated and you can view more information on this here: Your home phone is getting an upgrade.
I can see you were recently in a private conversation with another agent and they have advised that we have already migrated your mum over to the new system meaning in order for her landline to work, she must connect it to the hub we have provided. The landline will no longer work when plugging in to the wall socket as we no longer provide this method.
Looking at the account this end, I can see an engineer attended and got things resolved too.
If the handset is connected to the Hub but it's still not working, come back to me here and we'll be able to book another engineer however if we book an engineer now and it turns out the phone has just been plugged back in to the socket then a £25 charge will apply.
Please check this and come back to me asap so we can help further.