Avoid any business with Norman Bisset

Norman Bisset keep sending me reminders to pay an amount to ADT, which I do not owe. I've even sent them a copy of an e-mail from ADT admitting that they owe me money. No response from Norman Bisset, but then another veiled threat again a few weeks later. They either don't care to read e-mails addressed to them, or think if they keep wasting my time I'll eventually just pay them to make them go away.