We recommend having a read of these community articles, which may help with your concern:
I've managed to locate your account using your Community details and have detected no line fault that can affect the homephone service.
I have since organised a call back to be made today, 03 May 2021, from a member of our Technical team to assist you in checking for any underlying cause of the issue.
We apologise for the inconvenience.
The case is still being investigated by our Network engineers as they've encountered an issue with the service.
Further updates will be given by your assigned engineer as soon as it becomes available.