Phone giant 3G had applied for planning permission for a 15-metre base station on the car park of the derelict Blidworth Miners' Welfare building on Mansfield Road.
Newark and Sherwood District Council refused the application — but under new national rules a phone company must be notified of the decision within 56 days or the project can go ahead.
It was revealed this week that planners informed 3G on the 57th day, meaning the mast could be installed despite the no-go ruling.
Said head of planning Mike Evans: "Because of that hiccup we approached them and as a matter of goodwill had hoped that they would reconsider –– or at least meet us.
"But no, their attitude was 'we've got consent and we're going to erect it'. We're very disappointed."
But 3G bosses say they have done everything they were required to do — including asking relevant bodies for their comments before the planning application was even submitted — and insisted they are doing nothing legally wrong by putting up the mast.
Said spokesman Verity Blake: "It is regrettable they didn't contact us within the time frame as this causes problems for all parties."
Furious resident Susan Evans lives opposite the mast and has criticised council chiefs this week for their blunder.
"The council has been inept — it informed residents that planning permission had been refused but didn't get a letter to the company in time," she said. "The council's incompetence needs to be shown up."
Mrs Evans and her husband Bill now plan to lodge a complaint with the Local Government Ombudsman and say they are also considering legal action.