They can fail you know?
Before going to deep check the splitters, check the cables are in good condition no fraying or damage of any kind. Also make sure they are correctly plugged in.
Have a look at the phones, could be a daft a thing as one of the phones of the hook.
Is the broadband wireless and are any of your phones wireless?
Also whats the total ren value? Each phone and router on the line will have a ren value if you exceed it then your get problems.
When did the problem first happen?
Did it always happen at first or get worse as time went by?
I was shadowing one of our engineers today and two problems customers thought were major issues were a cable unplugged and a sensor not behaving correctly. Both with simple fixes, but the clients both thought they had major problems
Both of which had I.T experts
because they looked at the issue to deeply and didn't check the basics.