A warm welcome to the forums. Is this a new phone number / one ported in from Talk Talk or Sky? If yes it might take a little while for the dsl checker to acquire knowledge of the number. Can we please cover off some of the basics first...
Broadband is not going to work well if the "phone" line is not working properly.
Please perform a quiet line test - dial 17070 select option 2 using a corded phone plugged into the test socket behind the face plate of the master socket. It should be silent. A noisy phone line (or no dial tone) will have a marked adverse impact on the performance of broadband.
If the line is noisy or there is no dial tone, then a PHONE LINE fault needs to be raised with your phone provider. If this is PlusNet, you can report a fault on line using the button below.