ckuan is likely correct, there are many places to enter an Apple ID on the same iOS device, and they don't have to be the same ID. For example, you might be logged into iCloud with your new ID, but how about the iTunes & App Store? How about Game Center? Even Messages and FaceTime can use an ID that is different from your iCloud ID.
The other possible issue is that you have iTunes and/or App Store purchases on your device from your old ID. You will continually be pestered about those since you're using a new ID, with no way to transfer purchases to the new ID.
Rather than creating a new ID, perhaps it would've been better to have simply changed the email address associated with your original ID. But if you've created a new ID with your current email, you will not be able to (now) to associate that email with your old ID.