Two landline phones - neither working

Hi, we have two landline phones. The display on the second phone reads 'Check phone line'. We've tried another phone in it to check that it's not the phone and we get the same display, so the issue is definitely with the phone line. No problem comes up when I run a test. The main phone now can't receive calls - callers either just hear crackling or the call cuts off immediately. Sometimes we can call out, but other times there's just crackling. How do I arrange for an engineer to visit? This is my 87-year-old mother's only way to contact anyone so it's worrying.