Earlier this week, a man managed to get past security at her 6 million pounds mansion, reported Daily Mirror.
Contostavlos sent her personal assistant, Gareth Varey, to answer the door and there was a heated exchange.
"He started knocking down her front door in the middle of the night and Tulisa was utterly petrified. This is the last thing she needs to be dealing with right now. She has had an absolutely hellish past few days - and now this," a source said.
"She is at an all-time low. Tulisa is a girl whose professional life is in tatters. This guy started hounding her daily since the drug fixing story broke."
The man fled after the police were called but officers were able to track him down and arrest him. The man has since been released after being issued with a warning for harassment.
Hertfordshire police confirmed they had arrested a 24-year-old man from Stamford Hill in North London.