Wannenburg was the subject of a second complaint, this time from Vector, the following year, but there was no disciplinary or performance process initiated.
The ERA said these two complaints were normal in the course of an employment relationship and that Wannenburg's technical competence was highly regarded - something reflected in his promotion to the role of lead consultant in 2016.
Later in 2016, Theta installed a performance improvement plan after a complaint from TVNZ. The TV network said although Wannenburg completed quality work, it was concerned about the volume of personal calls he made and generally being away from his desk.
Wannenburg was called into a meeting about his performance last November where his managers reached a "consensus view ... that there was a loss of trust and confidence in Mr Wannenburg to make the change that was required of him".
At a follow-up meeting days later, Wannenburg was dismissed.
The ERA found that the process Theta followed in dismissing Wannenburg was "far short of what is required in cases such as this".
"Full details of the customer complaints were not provided to Mr Wannenburg at the time of occurrence. There was not an investigation by Theta of the complaints."
The ERA said the managers had relied on perceptions they had of Wannenburg's behaviour, rather than his behaviour itself. He furthermore did not receive any verbal or written warnings.
Wannenburg sought $25,000 compensation for personal grievance after the dismissal, saying he felt "humiliated and broken".
The ERA awarded Wannenburg $20,000.
Wannenburg also sought lost remuneration. Due to his being dismissed immediately before Christmas, he was unable to find a new job for several months and said he and his wife were financially stretched.
For this, he was awarded $23,133.