It's known as "bill shock" — that horrible feeling you get when your monthly cellphone bill is higher than expected due to surprise charges.

A "sizable" number of Canadians still suffer from this affliction, largely because they exceed their data limit, says a new CRTC-commissioned survey.

The study set out to assess the impact of the Canadian Radio-television and Telecommunications Commission's national wireless code launched in late 2013.

The telecom regulator created the code in part to help consumers better understand their cellular plans and limit additional fees to help prevent bill shock.

Canadians are struggling to track how much data they use. - CRTC survey

For example, international roaming charges are now capped at $100 a month and data overages fees at $50 — unless a customer agrees to pay for more.

The measures appear to be helping some customers. The survey found that seven per cent fewer respondents experienced bill shock in the past year compared to 2014. However, 21 per cent of people polled said they still get hit with unexpected charges on their monthly bill.

TNS Canada conducted the survey by phone in September, polling 1,277 Canadian adults who have a cellular plan.

Blame it on dearth of data

Almost half of respondents suffering from bill shock (48 per cent) said data overage fees were the top culprit. Seventeen per cent blamed international roaming charges.

"This suggests that Canadians are struggling to track how much data they use" and "understand the cost of international roaming," said the report.

Overall, close to half of people surveyed (46 per cent) paid data overage fees in the past year. Seventeen per cent said they got hit with the added charge three times or more during that time.

Data overage costs on a monthly bill ranged between $50 and $250 for half of the respondents. A small number faced charges of more than $500.

The report also noted that cellular service and wireless data in particular have become an important part of Canadians' lives. Respondents said they used their phones to do everything from emailing to banking to online shopping.

When asked for comment on they survey, the CRTC said that it's holding a public hearing in February to review the wireless code. In September, the commission jump-started the process by gathering feedback from Canadians and posting the comments online.

Numerous respondents complained about so-called bill shock.

"Cellular providers gouge based on demand," griped one customer. "It used to be minutes, now it's data. Data is ridiculously overpriced and intentionally confusing."

Another wrote, "Most every bill is above and beyond with data charges and other fees."

Telcos offer tools

CBC News asked the big three cellphone providers — Rogers, Bell and Telus — for comment.

Rogers said that just this week it expanded its Roam Like Home offer where customers pay a fixed fee to use their phone when travelling.

All the three telcos said that they offer customers online tools to help customers easily manage and monitor their data usage.

While such tools can help customers control their data, critics argue it's not enough.

Some critics are calling for an end to data caps in an era when Canadians are using more wireless data. (CBC)

Some people who submitted comments to the CRTC called for an end to data caps.

"Data prices are outrageous! It's time Canada offered unlimited," said one person.

Vancouver-based internet advocacy group OpenMedia agrees. It wants the CRTC to mandate that telecoms offer more generous data caps and unlimited data plans at an affordable price.

"Canadians, just like people all over the world, are using more data than we ever did before, and that's going to continue to be the case," said OpenMedia spokesman David Christopher.

"So it's really high time the telecom providers kind of up their game."

In August, T-Mobile announced a new unlimited data plan. (T-Mobile/YouTube)

In Canada, only regional providers Manitoba Telecom Services and SaskTel in Saskatchewan offer unlimited wireless data plans. For both, data speed slows down after a customer burns through 15 gigabytes. SaskTel customers also must subscribe to other services.

Freedom Mobile, formerly Wind Mobile, also offers unlimited data in the sense that once you use up the amount you've paid for, you can use additional data for no fee — but at a reduced speed.

In other countries, unlimited data deals are becoming more popular. Some U.K. companies offer them, and two major wireless carriers in the U.S. — T-Mobile and Sprint — recently introduced unlimited everything plans for $70 and $60 US per month, respectively.

There are some caveats to both U.S. plans. For example, video streaming quality is limited to low-resolution.

Get rid of roaming fees?

Christopher also says the CRTC needs to address the issue of international roaming charges that are still running up the bill for Canadians.

He points to the European Union, which is eliminating roaming fees for cellular customers in member countries. Come June 15, 2017, they will be able to use their phone when travelling within the EU without incurring extra charges.

"When you roam, it should be like at home," said EU president Jean-Claude Juncker in a statement.

Christopher also says it's common for U.S. cellular plans to include free roaming in Canada without any extra charge.

"We've just got so much catching up to do here in Canada," he says.