Some detail of what your experience is (other than "horrible broadband") will help others to offer guidance.
Which broadband service are you using - ADSL or FTTC?
Which router are you using?
What are the line stats?
How are the devices experiencing "horrible broadband" connected to the router - Wifi or ethernet cable?
If WiFi have you tried splitting the bands?
What channel is the wifi using? (Auto or a specified channel?)
Have you run a QLT?
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. From the Q&A list, choose the one which matches the problem, 'open' the 'section' and click the trouble-shooter link. NB: If you receive a failure message (rather than a log-in prompt) then log-in to the user portal in a different browser tab and attempt to use the trouble-shooter again.