Hi, if you are using broadband , then try changing your phone filter as they tend not to be the robust of hardware. This is the hardware that plugs into your phone socket - your phoneline/router then plugs into it. Also, check that your filter is on your Master phone socket (usually that is nearest to the entrance of your house). lastly, EVERY phone in your house should be plugged into the phone socket via a phone filter (i.e, one filter per phone socket).
Hope this helps.