Echo on phone calls to France

[#1]

which my mother complains has just started since she switched to plus.net talk anytime from BT earlier this month. She's had plusnet broadband for several years. It can't be connected to this switchover can it?
She's been calling my sister in France for years with no problems, and now has echo. She's quite deaf and has a cordless Panasonic DECT KXTG 7160. Any suggestions on how to sort?

[#2]

Hi
It could be the DECT, A neighbour with a simular base unit, try on a corded phone to rule out the wireless first.
IAn