The original contract persists, it has simply been assigned (and in this case, assigned in the legal sense means sold, not simply "placed") and all your obligations go along with it.
It's entirely legal... (see s53 of the Conveyancing and Law of Property Act)
http://www.canlii.org/en/on/laws/stat/rso-1990-c-c34/latest/rso-1990-c-c34.html#BK52
They aren't allowed to add "fees" though (like "collection fees") unless you also agreed to that.