Landline making a screaching noise when answered

Last week my landline was completely dead with no dialtone. I booked an engineer on Saturday who came & fixed 2 faults with the line. Shortly after he left the incoming call just screaches so i'm unable to make or receive calls. I tried to book another visit but i'm unable to do so as it says i have an engineer booked already . Sometime when ringing in for a mobile i get a constant engaged tone. There is only one phone plugged in at the property.