My internet disconnects when i use the phone this has been a on going problem,it just drops connection randoml?

also when i dial a number on my landline the internet gos orange then thew seconds later back blue again,ive had 3 engineers out and now they rang me today and said theyve updated the exchange,theyve done lots of things but my internet still drops???ive changed routers still the same,it wasnt doing it when i first had bt broadband but now its been happening for 3 weeks,can anyone help?