The judge said McCartan had all but been imprisoned her in her home last August.
McCartan had "outrageously violated" her constitutional rights by engaging in "deplorable conduct," and had engaged in behaviour "which in a civilised society cannot be tolerated", the judge added.
The High Court judge had previously ruled that Ms Sullivan was entitled to a permanent injunction preventing Mr McCartan from contacting, watching or besetting her.
Ms Sullivan, represented by Yvonne McNamara, brought proceedings against McCartan, as well as against Gerard Boylan and Gerard Boylan Building Contractors Ltd, Drumboat, Inniskeen, Dundalk, Co Louth, who had hired McCartan. The judge said Ms Sullivan engaged Mr Boylan and his company to carry out building works at her property, which concluded in May 2012. She paid them €84,000. However a dispute arose over whether certain works had been carried out.
The Boylan contractors hired McCartan to recover what they claimed was a debt owed to them of €20,000. The debt is disputed by Ms Sullivan.
The judge noted she initially thought McCartan was an intermediary.
However, she got an email from him demanding payment.
McCartan sent her texts and emails in early August demanding payment of the debt claimed by the builders. McCartan also made telephone calls to her.
One message stated "My calls and presence will continue. I will embarrass you to your neighbours if you continue."
In another email she was told to "pay up and save yourself all the embarrassment".
In late August, she received an email from McCartan saying he would be "in attendance" outside her home due to her failure to settle up.
McCartan said he would also "start knocking on doors and telling her neighbours" until the money was paid.
When she arrived home she found a van, with the sign Licensed Debt Collectors prominently displayed on it, in front of her house.
Gardai were called, and held discussions with McCartan. He then left, but the gardai told her they were powerless to stop him returning.
The judge said that despite being asked to desist by Ms Sullivan's lawyers, the harassment continued.
Greatly upset and frightened by this, Ms Sullivan sought, in late August, an injunction against the debt collector and the builders. The judge said the Boylan parties gave the court appropriate undertakings, and ended McCartan's retainer.
The judge said what was objectionable about McCartan's conduct was its persistent, premeditated, unyielding and oppressive character.
He ordered that McCartan should pay Ms Sullivan general damages of €15,000 and a further €7,500 exemplary damages for his behaviour.