Citizens Advice has called on the mobile phone industry to do more to prevent shock bills, saying companies are "hanging customers out to dry".
The advisory service said 28,000 issues relating to mobile phones and contracts were reported last year and a further 102,000 people sought help online, with complaints including shock bills, phantom charges and billing errors.
The new figures come ahead of World Consumer Rights Day tomorrow, with this year's theme being mobile phones.
Citizens Advice said some customers had been hit with "shockingly high" bills after making calls abroad or using the internet, or as the result of scams or having their phone stolen.
Complainants included a woman who received a £2,000 bill after she used the wi-fi in a hotel lobby in the US.
Her mobile phone operator insisted she pay as her data roaming was not turned off and she did not buy a package before going.
Another complainant took out a loan to avoid going £408 into debt with his bank after a billing error meant he was charged more for his mobile phone costs than he should have been, but was initially only offered an apology when he complained to his provider.
Citizens Advice chief executive Gillian Guy said: "Mobile companies are hanging their customers out to dry with shock phone bills. Some people are facing bills of hundreds or thousands of pounds. Others are being driven into debt as they struggle to cope with these unexpectedly large bills.
"The 28,000 issues reported to Citizens Advice in 2013 shows people are experiencing a myriad of problems with mobiles including faulty phones, services that are not up to scratch and misleading practices.
"It's time the industry looked at how it could banish bad behaviour and help customers avoid large bills.
"Phone providers could help people by sending them text messages with reminders about the costs and any limits they have. There is also an opportunity for firms to be innovative by creating tools for people to keep day-to-day track of their charges, calls and data use.
"Consumers can also take steps to steer clear of running up a large bill abroad including checking costs with their network before they travel or getting a local sim card if you visit a place regularly."
There is a limit on how much phone users can be charged for data while in the EU, and Citizens Advice said it wanted to see the cap extended to countries further afield.
Citizens Advice Scotland chief executive Margaret Lynch said: "The consumers that speak to us often feel powerless in the face of problems with their handset, shock bills or unexpected changes to their contracts, compounded by poor customer service from their operator.
"Citizens Advice Scotland's services are here to help with free and confidential advice from our consumer helpline, self-help advice online or our network of local bureaux."
Consumer Minister Jenny Willott said: "Nobody wants to be stung by sky-high and unfair charges on their mobile phone contracts.
"This is why we've come forward with strong measures to introduce a cap on bills when phones are lost or stolen and stop unexpected mid-contract price rises.
"If people think they are getting a harsh deal then they should get in contact with Citizens Advice, who can advise them on their rights."