What to do about phone/internet companies that harass you, AND keep on billing you after the account has been closed?

I’ll try to make this as simple as I can, with only the details I believe are needed; my roommate and I recently switched from Bell Canada to Videotron. (phone, cable and internet providers)

My roommate is in charge of paying for that, and it’s all her account. She hasn’t paid for the last Bell bill though, which is 105 dollars.

So A) They won’t stop phoning here all day, which we can’t really complain about, because it is money she owes. I told her to give a definite date to when she’ll pay, but she doesn’t know when she can, so until she does, I don’t think there’s anything to do about this. I don’t have a job right now, so I can’t lend the money, and she has work, so I told her it’s up to her to rectify the payment. However they phone here like five times a day on weekdays, and this particular company has a very bad reputation for this kind of thing.

However there is a B) and this is where we need help. She received ANOTHER bill, which now amounts the whole thing to 234 dollars. (this company doesn’t add interest to late fees, never heard of no phone company that did, either) She CANCELLED the account like a month and a half ago, and they’re billing her for dates that haven’t even HAPPENED yet. (even though her account is closed, and we therefore haven’t used their services) This last bill she got goes into the first week of December. What the hell is this? We’re not even with them anymore, and we’re not even in damn December yet. O_o

So I told her I’d look online to try and see if I can find some information about both the phoning harassment and the phantom bill. Isn’t there something that can be done? I remember looking this up years ago, and this Bell company came up and they had phone numbers you could phone for company frauding and phone harassment and stuff, but right now, I can’t find anything that isn’t dated almost four years ago. Is there anything at all to do? (there was a similar story to this where a women kept on getting bills from them for almost a year after she cancelled her account)
The only thing I can suggest her is to tell them a certain date for the payment, (then we can really bitch if they don’t stop the phoning, at least in between now and the date she specifies) but now she has this extra bill for services that weren’t used, there has to be some law against this. Help? And this is in Canada, so please keep that in mind if you have any suggestions. Thanks.