Landline constantly engaged, can't make or receive calls

Hi, its been 4 days now that my landline has been constantly engaged, every time I try to make a call the number I'm calling is engaged (have tried lots of different numbers) and if someone tries to call me all they get is an engaged tone.

I have tried doing all the resets etc. but nothing works.

Can someone please help me with this as it is urgent.

Many thanks

Dan