A frustrated man who "blew his top" at a call centre operator and threatened to "exterminate" them after being mistakenly chased for a debt has escaped serious punishment from a sympathetic judge.

Brendon Arnold phoned call takers working for Receivables Management NZ on November 29 last year to complain that he was being wrongfully pursued for a debt that wasn't his.

But the 55-year-old Christchurch man soon lost his cool and started abusing and threatening the call taker who tried to calm him down before hanging up.

Arnold rang straight back and demanded the full name and address of the call taker, who again ended the call.

A minute later, Arnold phoned back, demanded the address of the business, and told the call taker that he was going to "exterminate" them.

Later, Arnold explained to police that he was "uncontrollably angry" about being harassed and that he didn't owe a debt.

Today he pleaded guilty at Christchurch District Court to a charge laid under the Telecommunications Act of offensive use of a telephone.

Defence counsel Tony Garrett said while Arnold was apologetic, it wasn't surprising that, as he told police, he just "blew his top".

Judge Jane Farish said she could understand why he lost his temper.

But she reminded Arnold that if he loses his temper, he must keep expletives to a minimum or else he'll end up in court.

In the circumstances, she agreed that a conviction and discharge was appropriate.

Arnold thanked Garrett as he left the court.