Both TalkTalk and BT have agreed to change their processes following the mystery shopper tests.
Other providers such as Sky, Virgin and TalkTalk have increased prices in the last six months.
During the second quarter of 2012, it received 0.53 complaints per 1, 000 of TalkTalk's customers.
In broadband, TalkTalk generated 0.42 complaints per 1, 000 customers, again above the industry average.
TalkTalk remains the most complained about landline and broadband provider, according to UK regulator Ofcom.
That, of course, includes all of BT Openreach wholesale customers, like Sky and TalkTalk.
TalkTalk, which has topped the list since Ofcom started compiling it in 2010, slipped to second place.
Internet service provider Orange has knocked TalkTalk off the top position in Ofcom's broadband complaints chart.
Despite this, it added, complaints about TalkTalk remained above the industry average at 0.35 for every 1, 000 subscribers.
Despite TalkTalk topping the charts again, Ofcom said it was not planning to take any action at present.
Although it did better on broadband complaints, TalkTalk generated the most negative feedback about its fixed landline phone services.
In the UK alone, for example, its customers include BT, Everything Everywhere, O2, Orange, TalkTalk, Virgin Media and Sky.
TalkTalk and BT were the worst offenders, offering users a speed estimate without prompting in fewer than half of cases.
Best Buy is not buying any of Carphone Warehouse's broadband or telephony operation, which trades under the TalkTalk and AOL brands.
Top 10 brands with the lowest percentage of positive mentions (descending): Microsoft, HSBC, Santander, Vodafone, McDonalds, T-Mobile, KFC, Barclays, TalkTalk and BT.
TalkTalk was second in the chart of most complained about broadband ISPs.
YouView - formerly known as Project Canvas - is a partnership between BT, the BBC, ITV, Five, Channel 4, Arqiva and TalkTalk.
"TalkTalk demands high standards from the companies it works with and as a result TalkTalk immediately stopped using these suppliers, " said a spokesperson.
Tweets issued by accounts linked to Anonymous also claimed TalkTalk was targeted over the weekend, although the network could not confirm the details.
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TalkTalk, Sky, Virgin, O2 and Everything Everywhere have already cut off access to the site, which hosts links to pirated music and video.
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YouView is backed by some of biggest names in British TV and broadband: the BBC, BT, Channel 4, Channel 5, ITV, Arqiva and TalkTalk.
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TalkTalk said it was fair that Ofcom had imposed the fine, and blamed the two call centre operators concerned, Teleperformance Limited and McAlpine Marketing Limited.
Other residential providers include Adept Telecom, Axis Telecom, Eze Talk and iTalk, while TalkTalk Business, Titan Telecoms and Optimum Calls offer ARCs to business users.
The letter, which was not intended to go public, was sent to six ISPs last week, namely BT, Sky, Virgin Media, O2, EE and TalkTalk.
There's no specified channel list just yet, but we're sure TalkTalk and BT will be filling us in on all the details ahead of any launch.
So perhaps the fact that the two businesses and the likes of Sky and TalkTalk - are scrapping so furiously over the broadband market is good news.
Customers who subscribe to Sky Movies via Virgin Media, UPC and TalkTalk will also be able to enjoy the full range of subscription films from the NBCUniversal collection.
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The code will be piloted by BSkyB, BT, O2, TalkTalk, Three, Virgin Media and Vodafone during 2011, with a review of how it is working in the following year.
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He said that many of BT's new customers were probably coming back from TalkTalk - which lured millions away with bargain basement broadband when it got into the business.
Better still, YouView promises to launch multiple new internet channels (through providers BT and TalkTalk), adding to the 70 broadcast channels available on the box at the moment.
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