The data overages are billed at $5 per 100mb for the first 1500mb. After that it is .5 cents per 1mb which is basically $50 per 1gb. It is billed per 1 line. It is also billed on a first come first basis. So if you if the first person uses 3.5gb and the next person only got to use 500mb of the plan and the third person uses 3.0gb then stops. No one has incurred overages. Now the second person who barely uses anything goes to open safari and bam they get that first charge of $5 per 100mb. Then the first and third person also go to use data and they also get charges. And so on and so on. It's not just Telus. They are competitively priced with the market. Here are the policies on Bell and Rogers websites.
Bell: actually while researching this it says on bell's website their overage is .07mb. Yikes! With their activation fee of $25 per line as well. How did I find this? You just go their website. Shop> rateplans > share all plans > I clicked on smart phone, picked the canadian plans > 4gb of data and it's in the tiny print at the bottom.
Rogers:
$7 per $100 mb per line.
There is some good news for you though. Telus has the cheapest rates and you don't need to switch carriers. The CRTC has mandated changed effective December that only the main line can be charged and it can't be per line anymore. This will probably result in prices going up but, there's been no word yet. Maybe not. What you want to do is utilze the Telus app! There's the data manager section in there where you can control who is blocked at what overage rate. You can also monitor the usage of everyone's line. And add the $2 data block feature when one person is being a data hog. It's $2 monthly which is prorated. It's basically 6 cents daily. You can also set it to drop off when the cycle resets. 
Data is really hard to control with multiple users. When only the owner of the account is responsible for paying the bill for everybody, you'll never control data unless you block them. That's the unfortunate nature of share plans--paying and making enemies. Me? I only share with myself. 
I think I have an obsolete plan though, 500mb, that I'm sure Telus will take away from me very soon.
BTW, my flower icon is obscenely huge on all of my browsers lately. Is it trying to tell me it's been discontinued???? Lol. My luck.
@Mobility_Princess-- From within my Shaw account I have links to chat (with voice), email, phone numbers, online support, service updates, all listed very clearly in the sidebar. Plus of course there's Facebook and Twitter to reach them.
For email, the message says: "If your situation isn't urgent fill out the form below and an eCare representative will get back to you within 48 hours."
And really, many, way many situations are not urgent. Last week I altered my TV package (we can add services online, but can't remove services online) and changed my contact phone number. I love being able to shoot off my email and get on with my life. 
It's important though to really detail what you want, or the help you need.
Telus mobile is great for the ability to email. I just got my contract // billing error settled by email, 30 emails in all, and it gave the Telus rep and then the team a chance to really look into it without time pressure. I was in no hurry. I do think if a rep or team can take their time, they work better. Most issues are not emergencies.
