Unsavoury practice by Fedelity-Adt

I am sick and tired of ADT Security. They have been sharing my personal information with dept collectors as if it's a sport. I had an account with them and only terminated my account with them in 2015, having payed them full term. At first they hasseled me over the removal of the system at the house, stating that the signal from the system is confusing their guards when they respond to complaints in my area. Wow. I complained, called their HO and then placed my complaint on Hellopeter. They never even bothered to revert back to me. Secondly, since 2017, I have been haunded by dept collectors stating that I owe ADT. I took it up with ADT and they emailed to confirm that they incorrectly handed my account over. So the calls stopped for a while till October 2018, I have been receiving smes, emails and called from collectors on behalf of ADT. Today I got yet another call from a lady working at Credit Worx. ... I even sent her an email I received from a Pelediso Damane an Executive Escalation Officer at Fedelity-ADT. In this email, the sender stated that my account was handed over in error. It is clear to me that this company does not reconcile their work. Why am I being harrassed? How does all this impact my credit score?