Broadband not working until external call made

Hi, wonder if any experts can help? My mothers broadband keeps dropping off and not working, strangely if she makes an external phone call it starts to work again and makes a broadband connection. This can last for anything from a couple of mins to the rest of the day.

She's had a new router and filter supplied and the same issue occurs. Any suggestions? Assume it has to be the box coming into the house or something to do with the line?

Thanks

Most likely a joint or crack in cable and the extra current from the call is enough to clear oxidisation and allow broadband to work again.

Needs provider to get someone out to look at the state of the line

As MrSaffron says, but worth checking there is no damp at the back of the master socket. And/or the socket she is using.

If the OP is testing into the master socket, extensions disconnected, then yes I agree.

Using the line to force sync is the lesser known symptom of an HR fault.