An unemployed mother-of-one was unknowingly charged £4,000 for photocopying by her divorce lawyer, the legal watchdog has revealed.
In a study of legal complaints made against divorce lawyers, the Legal Ombudsman said the woman, who had been made redundant, asked her lawyers to halt proceedings but they continued regardless and hit her with a £15,000 bill.
The woman - known as Miss A - brought her complaint to the Ombudsman, which agreed the firm should waive the final bill and ordered it to do so.
The study revealed that nearly one-in-five or 18% of the 7,500 complaints resolved last year were about divorce or family law-related cases, making it the most complained about area of law in England and Wales.
Chief Legal Ombudsman Adam Sampson said: "Clearly lawyers could be doing more to reduce complaints by providing accurate cost information, providing decent service levels and by taking complaints seriously.
"I think this report challenges lawyers to raise their game and make the divorce process less painful for consumers."
The Ombudsman said it found some cases where bills exceeded divorcees' expectations by more than £30,000.
But it also warned people against running up unnecessary costs by using their lawyer to take out anger on former partners through the courts.
Dean Dunham, lawyer and founder of legal advice website YouandYourRights.com, said: "Instructing a divorce lawyer is no different to agreeing to use the services of a plumber - you need to know that they have the expertise you need, what they are going to charge and how long it will take.The report said around a quarter of divorce complaints related to poor cost information, with one in five - or 21% - saying they were not given an estimate of fees when they first consulted a lawyer.
"The Legal Ombudsman's report rightly challenges lawyers to improve standards and ensure that consumers aren't caught out by hidden or surprising costs."