So you became a Rogers wireless customer but brought your own phone that you bought yourself or had from some other source?
Did you get any type of compensation such as 3 months unlimited talking or data?
If you got nothing then call Rogers and explain that you never took the phone. You should not be under contract. I buy my own phones because I like to have the newest gadget and Rogers phones are usually a few years behind. A few months after I found myself under contract even though I shouldn't have been. I called Rogers and explained and they fixed it. Because 99.9999% of people take the phone the person entering it is so in the habit that even if you shouldn't be on contract they will still enter it that way.
Dealing with the collection agency will not help with the contract issue. That has to come from Rogers who will then lower the amount the collection agency is after.