I'm really sorry to hear that your phone line is extremely noisy, and crackling so bad it's impossible to hear people on the other end of the line. I'd also like to welcome you to the forums.
Thank you for letting me know that you've already checked all plugs and phones as this really helps with the diagnostics. I've done some checks from this end and can also see no explanation for this fault. So I'd like to look towards booking a technician to call out and investigate further for you.
I've sent you a private message in order to get things arranged, please look to the top right of this page where you'll see a purple envelope icon, click on this and you'll see my message.