Look determining whether or not there is a fault on your phone lines or not is a relatively simple job, but like a lot of things in life.... experience and a dash of common sense go a long way.
A lot of phone companies will tell you that you need to take a blade to the screws on the termination box of your line and then fiddle about connecting your phone to the test socket that lies behind that said and for mentioned panel your removed from the phone termination point. this is just pure flim flam and.. and is just plain bosh.

Instead apply a little smidgen of common sense.... provide you have not been drilling holes in your walls of chiseling away removing sockets from your walls or rebuilding the wall in which your phone socket resides,.....! then it it likely that one of two things have happened:
Either there is a fault with your phone or a device attached to that termination socket, (could be a fax machine or a phone extension) or
there is a fault somewhere on the line, that includes anywhere on that line and could even be back at the telephone exchange.

Firstly, take out everything that plugs into your phone termination socket, i mean absolutely totally everything. Now, take your phone, and plug that into your main socket, (not an extension socket that bill installed in the summer house back in 1973... no the main socket). Check two things, is there anything displayed on the phone eg; something that says check phone line, and secondly lift the receiver and listen i mean really listen hard, is there a crisp loud ring tone........ or is there something else.