Harrassment and treatening by Alliace Dept Collectors call agents

I have been harassed and threatened by call center agents from Alliance Debt collectors. Different call center agents from this company are call me every now and then stating that they have an account from National Security company in my name that I am not paying and they are calling me to pay it. Even if I have explained to then what happened, confirming with National Security if I am not owing them and agreeing with Alliance to remove my number from their system they still call and harass me. They will be quite after a few calls every month and another agent will call me the following month. latterly they are sending me emails and SMSs stating that they are trying to get hold of me regarding outstanding balance on your NFS Account. The y say I should contact them immediately at *** or WhatsApp to ***