Phone line is being tapped. Who could it be and how can I stop it?

For the past few months, I have noticed that about 70% of my phone conversations are being tapped into. When I'm talking to the other person I can hear a receiver being picked up from an outside line and I can also hear my conversation becoming a lot louder/ hear myself speaking at the other end. Just the other... show more For the past few months, I have noticed that about 70% of my phone conversations are being tapped into. When I'm talking to the other person I can hear a receiver being picked up from an outside line and I can also hear my conversation becoming a lot louder/ hear myself speaking at the other end. Just the other day I was talking to a friend then heard someone tap into my line and cut off the bloody conversation! I'm getting so f*cking sick of this. I've discussed it with my parents who don't seem to bothered about/affected by it as they only use the phone for brief conversations. I know nothing about technology so would be grateful if someone could give me some information on phone tapping like: who's likely to be tapping in to my phone line? And how the hell are they doing it? Also, how do I approach the subject with BT and what can they do about it?

Thanks for any advice.
Update: In response to those who think I'm some over paranoid criminal,I'm not! As I said, I know nothing about technology and I have every right to be dubious about people listening in on my conversations. I keep hearing someone picking up the receiver from an outside line however they do not put it down again.... show more In response to those who think I'm some over paranoid criminal,I'm not! As I said, I know nothing about technology and I have every right to be dubious about people listening in on my conversations. I keep hearing someone picking up the receiver from an outside line however they do not put it down again. Now they've started cutting off my calls so I'm entitled to be annoyed at this invasion of my privacy.
Update 2: One more detail, I live in a bit of a sh*tty area full of scummy people, hence me being very wary.
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