Do you have dial tone on your phone, and is there any noise on the line?
I don't actually have a landline, but when I ran the diagnostics it didn't say there were any issues with the landline.
The diagnostics are not accurate, you will need to plug in a phone, as its most likely you have a disconnection on your line somewhere. You can get a cheap wired phone for about £6.
If you do not get dial tone, or the line is noisy, then you need to report it as a line fault, and when its fixed, the broadband will come back.
So I've plugged in a landline and there is no dialtone on the phone. When I call the number it rings but I can't answer it. I've done the diagnostics on the landline as well now but that didn't find any faults.
That is the problem. You need to report that there is no dial tone, do not mention about the broadband.
When the phone line is fixed, the broadband will get better.
The line test diagnostics cannot detect a disconnection close to, or in your house. Its important to make sure you check at the test socket first, to avoid a possible charge.
Its possible your line has been disconnected in error, or has developed a fault. That is why it was important to check with a phone,
That should be sorted out early next week, as phone faults are usually fixed quickly. Probably just a broken wire somewhere.