Sorry I saw this and thought someone else would tell you this as it's quite straightforward really. When you're contract ends, it 'should' be rolling or ongoing until you decide what to do next. In my case, they kept me on the same contract without the 'extras' that were given to me through my last upgrade (text pack and money off). I say 'should' like this as CPW will probably try and convince you that you have entered into a brand new 18 month contract. This is not the case - you can cancel anytime you want (30-day notice as per normal contract conditions) but you won't get charged.
If I was you, I'd contact your network directly (ignore CPW) and ask what they will offer you to stay as you want away from the middleman in this equation. They'll offer you a pretty good contract and you'll get less hassle. However, you may opt for the 'money-spinning' problematic free gifts from CPW or other retailers, but if you do, I'd cancel your current contract and go in as a new customer as the deals are better this way I believe.