I get disconnected

Hi im based in the U.K and my problem is when someone phones my landline my internet connection goes off

ive had no trouble for years but 4 weeks ago I changed how I pay my landline I kept my BT line but I pay my landline phone bill to post office

My internet broadband provider is orange/EE

ive also got filters in living room and my bedroom

My router is Netgear DG834G v5

ive also got two smart TVs that use internet