Callers are regularly forced to wait more than half an hour to be connected to council advisers – and are being billed for the delay.
The average time taken to get through to Aberdeen City Council’s helpline is one minute and 41 seconds, figures obtained by the Press and Journal show.
But the longest recorded waits are all over 30 minutes and the authority said such periods on hold were “not uncommon” at the busiest times.
The council uses cheaper 030-prefixed numbers, which are charged at local rates and included within many “free minutes” packages.
Calls from BT landlines though cost 11p per minute and Ofcom says calls from mobiles can cost between 3p and 40p per minute.
That would mean 34 minutes on hold could result in a bill of anything from 68p and £13.40 for some mobile users.
A council spokeswoman said: “Call handling times at the customer contact centre for the first six months of 2016 are on a level with last year’s figures.
“Our average wait time to connect is just over a minute and a half and this represents a good reflection of how we manage our call arrival demands and match that with enough customer service advisors to make our customers experience a good one.
“Our longest waits are not uncommon with peak demand especially on a Monday morning and we will always try to promote our other channels of service such as our website as an alternative method of engaging with Aberdeen City Council for certain types of enquiries.
“Whilst we work very diligently to not leave customers waiting for a response, unfortunately, like many other large organisations, there are times when demand outstrips the resource.”
The longest wait in the first six months of 2016 exceeds any recorded in the previous five years.
In 2011 the record was 22 minutes 42 seconds, in 2012 25:40, in 2013 31:53, in 2014 25:30 and in 2015 32:34.
Councillor Ian Yuill, leader of the Liberal Democrat group, said such waits were unacceptable and called for action to reduce them – or give people the option to be called back rather than remaining on hold.
He said: “I am pleased that the average is so low but it’s not really acceptable for some people to wait for as long as they do.
“I look forward to seeing what is proposed to tackle the problem, and as soon as possible.”